Why write? The act itself is rewarding; to put down words, to try to articulate thoughts, feelings, emotions, to describe the world. It's a challenge and a calling. It's a way to experience, and re-experience a life (because I can?!?). Just like meditation, or running; the act of doing it, changes the one doing the doing.
It's about communication too. Putting words on paper, passing them to another pair of eyes. These things would not be said in this particular way, without sitting down and tapping them out on a keyboard. If everything is flowing, words come out, sentences take off, and the writer too, is suprised by where the words lead, by what they add up to.
Then there's the idea, vague, unformed, but out there: these words will live, maybe in someone else's head for a brief time, maybe for a long time, see Shakespeare, Beckett, Melville, Kerouac. Can some magic sequence of words lead to fame (overrated?), fortune (fools gold?), some kind of immortality (you gotta be kidding!)?
I'm hip to that, although, I feel like I have taken a much more Zen approach to my writing. Write and damn the consequences! Write and be a writer. Write and change a life. Just shut up, and fucking write!