I can say with honesty that a good many that were JW youths when I was growing up...are still in. *sigh* In one family (elder's kids), 2 out of 3 of the kids are still in, very much active, married other elder's kids, and are raising their kids as JW's. 2 who were friends of mine, same thing...married JW's and raising the kids in it (although...with one of them, her husband was questioning things awhile back...wonder what ever came of that?). Very few actually left and believe it to be a cult. As a matter of fact, only one other than myself that I can recall.
Maybe it's a regional thing...and an association thing. I find that those who have more association (that's supervised anyway) within the congregation tend to stick with it because they have so many friends and to them it really is a "Spiritual Paradise". They don't see the need to make friends with the "world", and so they're happy in their ignorance because they have a support system. I know of one group in particular that would get large gatherings together to go dancing and they never got into trouble.
Those who were on the outskirts (the "fatherless boys" and "orphans", for instance) don't really get that same level of association, so for them, they're willing to go "outside" to find it. This makes them more open to exploring other things. And then you have some elder's kids (like the son in the first family I mentioned) who get sick of the stringency and rebel.