Jerry Seinfeld has spoken about this himself. He never does college gigs because they have no sense of humor. Everything must be politically correct.
This age of p.c correctness on college campi coincides with the rise and dominance of females on campi. Females are now the majority of most of the nations's campi. It's well known that male (often very nasty) humor does not go down well with females.
Add to that the growth of the femi-nazis i.e liberal fascists who proliferate on college campi, and you have the ingredients of the p.c. culture where nothing untoward is permitted.