A lot of my life long friends are heavy drinkers. I wanted to give up the alcohol but not the friends.
In my case I tend to be pretty much a loner by nature and not very social. Drinking was an attempt, I think, to loosen inhibitions but it was not successful at changing anything for the better. Mostly it was just a lost decade. After I quit, life got increasingly better as each year passed.
Other posters have joked about waking up and knowing that this is the best you may feel all day. I actually appreciate the fact that I will never suffer another hangover.