For a number of reasons...mainly because I believe it is a poor example for my son, I don't like feeling like shit, and I dont even really care for the taste. I will still have a few drinks a couple times a year socially but that's about it.
I would much rather stay home with my wife and son than go out.
I used to party a lot tho...actually to the point I went in to the doc for a check up and they did blood work. When I got the labs back the lab had wrote on the report "no more party drinks" because my liver function taste was 5x the normal limit.