In many cases abusive parent(s), and not achieving in school; also having right friends, or not having friends, being turned off by the hypocracy. These are the main issues for kids in high school and post.
older people may not fit in the Shule(s) they live in, not attaining friends as an adult is just as difficult.
We should not be so quick to label though. Someone can’t go to Shule, let them sit home and daven/learn, we dont have to name call.