Each of us has different reasons for why we do it. Write, that is. It is, after all, hard work, and often for little reward.
When it goes right, nothing can give you greater pleasure. I have come to feel about my stories (especially since I started doing longer works) that the true satisfaction is in the work itself. At first, I wanted to sell, sell, sell, and I did publish a lot when I concentrated on short things. Now, I'm more in tune to making the writing as good as I can. The work is my reward, because I enjoy every minute, even the ones when I'm struggling hard. Then if it gets accepted -- great! If it doesn't, I've had my fun. My friend, mystery writer Helen Chappell, says I should be shot for even thinking such a thing and "nobody but a fool every wrote, except for money." But I can't help how I feel.
Yes, writing is hard. Some days you feel as if you're wrestling a bear. But, oh the sense of accomplishment when you make that bear dance!