Obviously YMMV but the reason I don't drink is that I used to.
I was born with one of those personalities/genotypes/whatever that lent itself to addictive behavior. Or maybe it was because on my upbringing. Regardless of why or how, by the time I quit drinking, it was all I was doing. I went to work, I came home, and I drank. I never drank at work, and my drinking never directly interfered with my work (although I was usually a wreck from 9 to 2), and I never got into trouble with the law. After work and after I did everything that needed to be done, I sat on the couch and drank and drank and drank. At parties I drank. Alone, I drank. I drank to be social, to be antisocial, to kill a hangover.
Finally, I was granted a moment of insight to where I saw what I was doing with my life. More accurately, what I was not doing. I chose to get off the couch, but I couldn't do it with a bottle in my hand. So I quit. 18 months now, and I am still sober.
Some people don't drink because when they do it consumes their lives. I know, because I am one of them.
Feel free to kill this or downvote it, but I feel like this was a point of view not well represented.