This is a more complex question than it may seem at the outset, even if we limit our scope to the American church. Apologetics is not taught in churches because ministers and other church leaders are either untrained in it, or they are philosophically opposed to it. The question, then, is why apologetics as an intellectual pursuit has been long ignored by Christian higher education and by church leaders. This requires that we deal with generalities about attitudes within the church and how they have developed through the history of American Christianity.
The church, of course, has been influenced by the overall academic and social environment. J.P. Moreland has provided an excellent analysis of how intellectual pursuits such as apologetics have been forsaken by the church as a whole.1 I also recommend Nancy Pearcey’s Total Truth. I will attempt to summarize Moreland’s evaluation here.
The great revivals of the 18th and 19th centuries brought with them an emphasis on quick conversion of individuals to Christianity without sufficient attention to instruction in biblical doctrine. The Christian life became more about the experience than the intellectual assent to the teachings of Christ and the apostles. Without intellectual grounding, many Christians fell prey to the rising philosophical views alleging that only empirical evidence can support truth claims. Higher criticism began to cast doubt on the inerrancy of the Scriptures. Darwinism challenged Christian teachings on the origins of man. The evangelical church largely responded to these challenges by abandoning rational inquiry altogether. Philosophy, as a whole, became rejected by the fundamentalists, who stood by the truth of the Scripture. Mainstream denominations, on the other hand, accepted modern philosophy and rejected the inerrancy of Scripture, viewing it as a spiritual guidebook only, not propositional truth. Instead of engaging the secularists, the fundamentalists retreated to the margins of society. As a result, the church has largely adopted a blind-faith position regarding the knowledge of spiritual truth. Rather than faith being seen as a response to reasoned evidence of the truth of Christianity’s claims, it has become contrary to reason altogether. It amounts to believing despite all the evidence.
Ultimately, the absence of apologetics in the church has to do with intellectual laziness, which is sometimes made a virtue in the name of “faith.” The effects of anti-intellectualism in the church have been disastrous. However, further discussion of these effects would go beyond the scope of the current question. Again, I advise that you read Moreland’s work. The good news is that in recent years, apologetics is on the rise. Seminaries and other institutions of Christian higher education are beginning to teach apologetics and Christian worldview studies. Authors like Charles Colson, Josh McDowell, and Lee Strobel have popularized apologetics. Nevertheless, great work is yet to be done if the church is to become more of the salt and light it was designed to be (Matthew 5:13), after decades of retreating to the walls of the church buildings in the midst of the intellectual challenges of the secular world.