I'm transitioning because I'm sick of living as a man.* I've only lived that way for so long because I was convinced that my only alternative was to not live at all, and while I've seriously considered that alternative from time to time, so far I haven't taken it.
The idea of living as a woman seems attractive, too, though of course I don't
really know what it will be like. (I've heard of a whole bunch of disadvantages that come with being a woman, too.) But I don't know that it would be enough if I were actually satisfied living as a man.
I
could continue living as a man, I suppose. I would be just existing, though. When I tried the "starter drugs" -- skirts -- life started going from black-and-white to color. And each step I've taken on this "road to perdition"

it's gotten better. I'm starting to look forward to things. Having started HRT 1.5 months ago, I'm now impatiently waiting for my face to look more feminine and for the "boob fairy" to come. Next comes full-time, and, and. There's actually a reason, beyond mere duty, for me to stay alive.
ETA:
* -- there are days when I actively hate having to be a man, and am positively jealous of the women I see. It feels like some kind of purgatory.