Why is every young person getting drunk and partying?

I found this really annoying, especially when I went off to college (I'm in the US). I just couldn't take it anymore. People constantly drinking almost every night. Friday from 6:00 pm on was a party, then your friends want you to get up early on Saturday to go tailgating and drink more! I'm 27 now but I still have friends that ONLY want to go to the bar to hang out. Nothing else and some of them are 30. I hate it.