Yeah, I couldn't completely figure it out. I was located in the most promiscuous prefecture in Japan (true), on a college campus, on a coed dorm, so I saw a skewed view of things. There were probably two to three guys for every girl at the school. There were lots of lonely, good-hearted guys. Some had just sort of given up. Lots of porn manga being delivered to our dorm.
Others would desperately wait for their their turn on the cock carousel. Beta orbit some slut until she breaks up with her boyfriend. Naturally there were "Chad Inazumachin"s that seemed to be with a different chick every week.
I really don't know about the women. Almost all the girls in my dorm were sluts. But not everyone was. My girlfriend was a virgin. She was convinced she was the last one left. But I don't think she really was and we talked about other girls we knew that probably also were.
In retrospect, I think all the rampant sex and drinking was because this was basically the end of their freedom. From then on they are wage slaves until death. Yes, basically no time for sex and meeting people after school.