A lot of students have fake IDs. Depending on where you look up the information it could be from anywhere from 32% (1) to 69% (2) of students surveyed, and keep in mind there is going to be a bias to lie since its technically a crime. Who knows how many more are borrowing a legitimate ID from an older sibling or similar looking older friend, or are just trying their luck that the bouncer isn't going to card tonight. At a big undergrad school, that's potentially a few thousand kids under 21 getting drunk a night even if a fraction of fake ID holders are capitalizing on their access. Then there's also the kids that prefer to stay in and play video games. League of Legends was the big draw when I was in 10 years ago, I saw kids put in serious shifts in that game in the study rooms of the dorms. All this being said, studying is often isolating and depressing and there are plenty of outlets for college students of every persuasion to put it off as long as possible.

1. https://www.veriff.com/blog/fake-id-statistics

2. https://www.thelantern.com/projects/2021/04/28/fake-ids-join...

That's US-specific, though. Most of the world has lower drinking age, with 18 being most common, I think - at least any country I know, other than USA, draws the line at 18 y.o. In those places, getting drunk and partying starts during the final year of high school.