Yeah, there are a ton of reasons why Animal House was the first.

Yes I said first, it's important to note that Animal House (1978) invented the the genre. Of course there weren't any before that because before that the college movie genre was entirely different. There was no template to emulate.

It was produced by the National Lampoon which had only started 8 years earlier, but was a spinoff of the long successful Harvard Lampoon which has been running since 1876. This magazine had long featured crude humor like this, but it was available really only on the Harvard University Campus.

It's also worth noting that prior to 1968 American film had to follow what was called the Hay's Code. This was before movie ratings (G, PG, PG-13, R, etc.). In order to not have government or regulatory oversight of film standards the big studios all banded together and decided to follow strict rules for acceptable film standards. A movie like Animal House literally wouldn't have been able to get distribution until 1968 and for a while after that the after effects still were in practice. Any studio, theater or working filmmaker who helped you release something like Animal House would have immediately been blackballed from all major film and television. You basically just couldn't make a movie like Animal House more than a few years before it was actually released.

Even if you somehow managed to get funding, maybe from a rich benefactor or something there was virtually no way to get it into theaters or anything like that. It's not like home video (VHS, DVD, BluRay) was even a thing yet either. VHS technically came out in 1976, but was pretty rare until the 80s. Animal House is actually one of the first movies to actually do decently well in the home video market though because people were ashamed to watch it in theaters, and it was considered so unique at the time.