I earned a degree from BYU some time back. I knew many LDS people who did not truly believe in the tenants of their religion, but they were as unquestionably LDS as those with strong conviction. People simply believe what their parents believe. In political science, it is a widely known fact that ideological socialization(IS) is acquired overwhelmingly through the immediate family. The percentage is high enough to spawn entire sub-fields trying to find out how else is ideology acquired(as obviously many people break away from their parents beliefs). Being part of a community affects almost all aspects of one's life. Like someone mentioned above, he sticks with the system simply because he believes it strengthens his family and imparts good morals on his children. In reality, of course, he's judging those virtues through his own IS. I for an example, do not think that Christian moral ideals are as desirable as secular ones. Thus, I would not value the part religion would play on their imparting.
Breaking away not only forces a whole new paradigm on a member of a species that values stasis over flux, but also requires giving up many important things. Most communities, even tolerant ones, have prejudices against dissenters, and changing views is in practice ostracism from one's niche.
What I'm trying to say is that specifics on why someone leaves are, in a way, irrelevant. Every person has doubts on the truthfulness of one's own ideology. Rejection of an ideology happens when whatever brain mechanism is responsible for evaluating information decides the downsides of leaving a religion are preferable to sticking with it. The actual intellectual justification for leaving typically evolve significantly, after the departure.
