I grew up with a pretty zealous bunch and most are still in and not just still in, but uber-active--full-time service. I know, weird, huh? Most did not have kids (a few did). When it comes to my close family, of the three kids in my family, only one is still in, and of my four first cousins, only one is still in. But the two who are still in (one sibling, one cousin) both are regular pioneers and both are female. The ones who left (one sibling, three cousins) are all male. So there's a gender thing there.
I think being super-zealous when you're young might increase the likelihood that you'll stay with it, only because you have so much to lose and you've given up so much. No education, no kids, no savings. What else do you have but the religion? It's sad.