Mostly because I have it pretty good right now. I've got a group of awesome friends, a really lovely significant other, and nothing but money and time. Sure I gotta work way more than I want to, but that's just part of life.
There was a time when I didn't have any of that though, and the only real reason I continued was because it's more of a pain to stop. Not to make light of suicide or anything, but when you think about the logistics of it all, it's really messy, isn't it? It's not even guaranteed to work, even if you use some of the more reliable methods. Regardless of whether or not it works, your family freaks out, your coworkers feel all guilty, and a whole ass investigation takes place. And if I go through with it and succeed, now I'm forcing taxpayers to pay for my life insurance, and everyone will remember me as that "kid who killed himself over some b**** who didn't want him."
Nah, I'm better alive than that. Even if I'm miserable while alive, that's the worst way to go. I'd rather jump on a grenade or something, at least then people will call me a hero.