John Gerstner in his church history series on the Ligonier site guesstimates that only 2% are classically Calvinistical when it comes to predestination and election. I think that might be about right. A case could be made for even less.
How is this to be accounted for? Aside from the explanation that so few believe it because it is plainly untrue, there is a sociological explanation, an explanation offered by Stephen Prothero in his book Religious Literacy. He simply blames it on The Second Great Awakening of the early 1800s.
The Second Great Awakening began on the American frontier where Methodism of a less Calvinistic stripe had its way. Moreover, it was a more egalitarian phenomenon, taking place as it did in Jacksonian America, with a bent away from the more elitist, thoughtful and scholarly ways on New England, where the First Great Awakening occurred. Revivalism was born and was soon adopted as a way of reaching both nonChristians and the slothful in church.
This new revivalism led to phenomenal growth in church membership, but it was growth of another kind. The Second Great Awakening was nondenominational in its spirit. During this time we have the birth of nondenominational voluntary organizations, which emphasized cooperation across denominational divides and encouraged different church groups to see each other less as rivals and more as allies. Examples are the American Anti-Slavery Society, the American Temperance Society, the American Bible Society, the American Tract Society, the American Sunday School Union, the American Home Missionary Society, and so on. That which divided Christians was downplayed.
Prothero makes the point that this growth came at a cost, and the cost was religious literacy. The Puritanism of the First Great Awakening went to great lengths to spread religious literacy. And while the evangelicalism of the Second Great Awakening promulgated Bible knowledge, it discouraged theological accuracy as a divisive thing that would check the spread of experiential Christianity. Of course, the rise of Protestant liberalism during this period could only help this slide away from theological precision.
This spirit of nonsectarianism became critical to the burgeoning public school movement. Whereas previously education was an instrument for theological learning, now it eschewed denominationalism and diminished as irrelevant those aspects of Christianity which gave rise to varying denominations.
By the time this process had had its way the Christianity of America is characterized by an emphasis on “core” beliefs, beliefs that could be listed on one side of an 8 1/2 x 11 piece of paper. And preaching followed the script. Gone were the sermons that instructed. Inspiration was in and precision was out.
Calvinism cannot prosper in such an atmosphere. The spirit of the age is against it. In spite of the amount of press Time magazine gives to the New Calvinism, it hardly shows up on the radar screen. To sustain consistent Calvinistical thought requires attention and instruction which must go far beyond the usual diet and appetite of American Christians. Indeed, in some circles we are taught that such a thing is bad and indicates a head religion rather than a true heart religion. The times have to really change for there to be any headway.
From My Heart, Out Of My Mind 
Jesus did not expect many to follow him. Do not his words in Mt. 7 and Lk. 13 describe how few would accept his difficult words and expectations? God is not the god of popular, American evangelicalism. He is one who offends the masses and appeals to few.
In I Timothy 3:15, Paul calls the church “the pillar and ground of truth.” Regardless of the possible nuances of interpretation concerning this verse, any interpretation will clearly arrive at the conclusion that one major function of the church is to preserve the truth. The nature of the church also dictates that this truth will be largely theological in nature.
Show me the church body which has preserved the theological doctrine of divine determinism. It does not exist. New Calvinists are a nearly invisible body of protestant Christians who happen to believe that God is the efficient cause of evil in the world, not human free will (as the other 98% of Christians do, not to mention the other 1500 years of ecumenical doctrine up to John Calvin). If Calvinism is the truth, and this scattered, dissipate body of believers is the pillar and ground thereof, then it would seem that Christ has been proven wrong in Matthew 16:18, when He declares that “the gates of hell shall not prevail against [the church].”
In fact, the scarcity of Calvinist Christians is quite telling of the doctrine’s logical fallacy. This is not to say that number of adherents in the Christian community is a surefire way of telling a statement’s truth or errancy, but when the statistics are this extreme, it certainly speaks to me about the heretical nature of the doctrine.
1.) The Church is “the ground and pillar of truth,” as you said. But you yourself admit that this is open to “nuances in interpretation.” Moreover, but what is the Church? According to Paul, the Church is “built on the foundation of the Apostles and Prophets, with Jesus Christ himself being the cornerstone” (Ephesians 2:20).
2.) There is never a single statement in the New Testament that a true church will defend, believe, teach, and confess every doctrine found in the scriptures perfectly. However, it is true that every true church will be a ground and pillar of truth, albeit imperfectly.
3.) You stated “show me the church body which has preserved the theological doctrine of divine determinism. It does not exist.” Actually, there are 41 or more Confessional Reformed denominations worldwide (e.g., conservative churches that hold to either the Three Forms of Unity or the Westminster Standards). There are many Predestinarian churches that are not Confessional (such as the Reformed Baptist, Reformed Anglican, Calvinistic Methodist, and Congregational Churches). So your statement is clearly false.
4.) Explain how you and I have both heard of the “New Calvinists” if they are “almost invisible?” Is being mentioned in Time Magazine the same thing as being “invisible?” And you do know that “New Calvinism” is not a denomination, yes?
5.) You are correct that Calvinists believe that the Efficient Cause of evil is God (as it is written “I make good, and I create evil”). Just to be clear on this: the material cause of evil is mankind, the formal cause of evil is to be either a vessel of wrath or a vessel of mercy, the efficient cause of evil is God, and the final cause of evil is the glory of God.
6.) How do you know that 98% of all Christians believe in Libertarian Free Will? Have you personally interviewed 98% of all living Christians? Or have you read a poll that gives you that statistic? If so, I would love to see that poll and a statement about how the poll was conducted. But it looks like you just made that statistic up.
7.) Before asserting that libertarian free will (and not the Decree of God) is the efficient cause of evil, please define libertarian free will, demonstrate that libertarian free will exists, list what actions libertarian free will is capable and incapable of committing, list an opposite of libertarian free will (if you believe an opposite exists), describe where libertarian free will operates, describe how libertarian free will operates, describe why libertarian free will exists, state whether God has libertarian free will, solve the problems libertarian free will poses for divine foreknowledge and divine prophecy, and solve the “Burdan’s Ass” Paradox. You must do at least these in order to prove that libertarian free will could even possibly exist to begin with.
8.) A few days after Jesus said that the “gates of Hell would not prevail” against his church, crowds deserted him, the Apostles were offended at him, Judas betrayed him, Peter denied him, his family had no faith in him, and the Sanhedrin executed him under the authority of the Roman Army with the consent of the public.
The gates of Hades never overcame the church, even though it was reduced at that time to only around four people: Joseph of Arimathea, Mary Magdalene, Nicodemus, and a thief on a cross. Likewise, the gates of Hades will never overcome the church, even if most “churches” preach a false gospel.
9.) Likewise, according to the book of Romans, there was a time when there were only “Seven Thousand” truly redeemed believers of YHWH. The entire Levitical Priesthood (excepting any priest who was one of the 7000) had embraced Baalism. Certainly that indicates that neither large numbers nor the existence of a well-organized ecclesiastical institution is a litmus test of Orthodoxy.
10.) If numbers cannot be a “surefire” way of establishing a movement as orthodox or heretical, how can numbers be a “certain” indication of heresy? If something is not surefire, it cannot be certain. Your statement violates two laws of logic: the law of identity and the law of non-contradiction.
11.) If being in a minority indicates a heretical viewpoint, are you claiming that Athanasius was a heretic because he was banished and because there was a time during which most of the bishops were Arian?
12.) If free will was part of Christian ecumenical doctrine for the first 1500 years of Christianity, then explain Canons 4-8 of the 529 AD Council of Orange Declare:
CANON 4. If anyone maintains that God awaits our will to be cleansed from sin, but does not confess that even our will to be cleansed comes to us through the infusion and working of the Holy Spirit, he resists the Holy Spirit himself who says through Solomon, “The will is prepared by the Lord” (Prov. 8:35, LXX), and the salutary word of the Apostle, “For God is at work in you, both to will and to work for his good pleasure” (Phil. 2:13).
CANON 5. If anyone says that not only the increase of faith but also its beginning and the very desire for faith, by which we believe in Him who justifies the ungodly and comes to the regeneration of holy baptism — if anyone says that this belongs to us by nature and not by a gift of grace, that is, by the inspiration of the Holy Spirit amending our will and turning it from unbelief to faith and from godlessness to godliness, it is proof that he is opposed to the teaching of the Apostles, for blessed Paul says, “And I am sure that he who began a good work in you will bring it to completion at the day of Jesus Christ” (Phil. 1:6). And again, “For by grace you have been saved through faith; and this is not your own doing, it is the gift of God” (Eph. 2:8). For those who state that the faith by which we believe in God is natural make all who are separated from the Church of Christ by definition in some measure believers.
CANON 6. If anyone says that God has mercy upon us when, apart from his grace, we believe, will, desire, strive, labor, pray, watch, study, seek, ask, or knock, but does not confess that it is by the infusion and inspiration of the Holy Spirit within us that we have the faith, the will, or the strength to do all these things as we ought; or if anyone makes the assistance of grace depend on the humility or obedience of man and does not agree that it is a gift of grace itself that we are obedient and humble, he contradicts the Apostle who says, “What have you that you did not receive?” (1 Cor. 4:7), and, “But by the grace of God I am what I am” (1 Cor. 15:10).
I’ve always thought it very telling as to the Calvinist mindset how joyfully they clap their hands with glee at their appearance in Time Magazine.
Calvinism in a nutshell: Imagine a missionary enters a village that has never heard the Gospel. He tells the villagers, “Before God created the world He decided that some of you would be saved and go to heaven, while the rest of you would be lost and go to hell.” When asked, “Why are some chosen to be saved and others not?” the missionary tells them, “It is purely arbitrary. Nothing you do, have done, will do, nothing you think or feel, has any bearing on whether you are one of the chosen or one of the lost. God arbitrarily saves some to demonstrate his mercy, and sends the rest to hell to demonstrate his justice. Glory to God!”
That is Calvinistic (and Lutheran) monergism in a nutshell. Makes John 3:16 appear quite meaningless.