I've never thought about that before, so I'll have to think about it more. But the immediate thought that came to my mind is a different reason. Maybe (just maybe) Christian kids are brought up to believe that the secular world will feel evil when they encounter it. Then they go to college and realize that drinking is fun, that lightning doesn't strike when you sleep in on Sunday, that you don't feel much different on a day that you do read your Bible than on a day that you don't ... and it's a whole lot easier to not. There are really nice people who don't go to church; in fact, I fit in really well (better?) with them. Christianity with all its self-denial is hard and doesn't feel rewarding (this doesn't even need to be a conscious thought) ... "slipping" and having fun isn't nearly as bad as it's always been made out to be.
I'm working on a theory that I hope to blog about later, but the gist of it is that one of the reasons that Christian kids succumb to the "overwhelming" tempations and arguments of the secular world is that they spend their lives in churches that condition them to believe that the secular world will overwhelm their faith, so when they make contact with said secular world, they are conditioned to believe that their faith can't hold up.
The gist is: we expect doing the unChristian thing to feel evil, and so much of the time, it doesn't. It feels natural. Satan, after all, masquerades as an angel of light. CS Lewis figured that out in The Screwtape Letters.
I dunno ... just a thought. Probably prompted by Rex's Sunday School class, going all the way back to the second lesson, that we have 2 counsels in the world, and we (counterintuitively) must choose to reject Satan's counsel that God is withholding from us what is truly good. We (now I'm preaching to myself) need to be convinced of what is truly satisfying. This upside-down Kingdom...