One reason is that the STDs you do tend to catch from casual uni sex are cured by a $20 pill, if that's even on your mind when you're drunk in someone's dorm bed.

"Shit, I got HIV/warts from hooking up" just isn't something I ever heard in uni. It just isn't part of the discourse. Those just don't seem to penetrate the uni bubble.

But everyone I know had to deal with the clap.