This isn't too much of a surprise. How else do you get tf out of your small, homophobic town and into a community of other queer people? College! And how do you keep yourself from having to go back to that town or being on the streets cause your parents kicked you out? Get a career!
A couple other comments here have said the same thing, and I strongly believe this is the actual reason. Queer people flock to cities to improve their dating pool and social acceptance. College is a legitimate way to move to a city (and meet other gay peers). Source: have a fair amount of gay friends.
On the other hand, if you already live in a liberal metropolitan area, it's potentially more likely that more of your peers go to college so you go too (no source here, just spitballin).
