Why Do Teens Abandon the Faith in College?

Paul Tripp in his book, Instruments in the Redeemer's Handstalks about a practice he calls "Fruit-Stapling", in which we staple good fruit to a tree with bad roots.  His point is that often in personal ministry, we never get to the heart of the matter.  Often times ministry is focused on the external, and neglects the internal.  Tripp applies this truth to teens leaving the faith in college.  Here is what he writes:

This is what happens to the teenager who goes through the teen years fairly well under the careful love, instruction, and oversight of Christian parents, only to go off to college and completely forsake his faith.  I would suggest that in most cases he has not forsaken his faith.  In reality, his faith was the faith of his parents; he simply lived within its limits while he was still at home.  When he went away to school and those restraints were removed, his true heart was revealed.  He had not internalized the faith.  He had not entrusted himself to Christ in a life-transforming way.  He did the "Christian" things he was required to do at home, but his actions did not flow from a heart of worship.  In the college culture, he had nothing to anchor him, and the true thoughts and motives of his heart led him away from God.  College was not the cause of his problem.  It was simply the place where his true heart was revealed.  The real problem was that faith never took root in his heart.  As a result, his words, choices, and actions did not reveal a heart for God.  Good behavior lasted for a while, but it proved to be temporary because it was not rooted in the heart