Most college kids wake up at the end of junior year/start of senior year and know that 'the real world' awaits.
Also once you turn 21, half the fun of drinking is gone
I did more than my share of partying from 18-21 and I wish I would have had your attitude instead of the 'norm'. My grades would have been better, my life would have been easier, and I'd be about 2 years ahead of where I am right now.
In my experience, in the real world, those who can't give up the party aspect become the wage slaves, working jobs that they have to work, not want to work, and never really being happy. Some finally get a clue but it can take a very long time, others never do.
The nice thing is that in college it IS like highschool and you are lumped with people that you normally wouldn't choose to hang out with, after you leave school, people are a lot more spread out and you can do your own thing a lot easier.