Why would they ever go to high school to begin with? Why not just drop? Same reason they all go - societal pressure.
Besides, being a disruption or a PITA does not mean you fail academically. You can do quite well academically but absolutely be a huge PITA to all your peers.
I think you overestimate the intellect and interest required to succeed in an academic environment. We don't live in some weird society where only the most intellectually gifted (however you define that) and most interested are capable of succeeding in college or academica.