For me two reasons
1. It's harder than you think. I failed a few years ago and now I want a completely solid plan before I try again. I'm giving myself six months to make a plan that has at least 95 percent certainty of killing me, because I don't want to fail again.
2. Guilt. Even tho I'm not close to my family and they've screwed me over, I feel a big amount of guilt about the fact that I'll leave them by suicide. I wish suicide wasn't seen as worse than any other type of death. I've been ill since I was 18 and I'm 27 now. I don't want to live out another 50 years barely able to do anything and I wish society would see, that. Things aren't going to get better for me.