several reasons, some bs, some not:
1.I'm shy. I have friends that I hang out with, but I'm not the type of person that goes out and picks up someone, in a bar, anywhere else for that matter, meeting someone brand new that wasn't introduced to me isn't something I enjoy doing.
2. I have a wierd schedule. I work nights half the week, and the days on weekends, days off are monday and tuesday. Some days I'm up by 9 a.m, some days I am up at 2 p.m. and go to bed between 3 a.m and 6 a.m. Yea it's kinda BS, but it'd be a pain in the ass for an SO to deal with.
3. I live at home and don't want to worry about family like gopunk said.
4. Physically, most women don't find me attractive. I know the line about confidence, and I actually have become confident in myself, not giving a poop about what people say or think. Check those lame chick mags, how many girls want a short fat guy?. One I can't do anything about, the 2nd, I'm too lazy to do anything about.
5. I don't want one. I put zero effort into finding a girlfriend because I don't feel like dating someone right now. This is the biggest reason, and the best I think. If it fell into my lap, maybe, but I'm not gonna try, cuz I don't care.
Well, more than I expected to say on the matter, but a complete answer nonetheless.