This is from a facebook discussion:
Why does one write? I loved stories when I was a kid, and I told madeup stories to my brother before I could write. When I could write, I wrote stories, and I have kept doing it.
I guess I think archy the cockroach's answer is the best one: "Expression is the need of my soul." Though I would add a love of stories.
I lose my passion for telling stories fairly often. I continue either because I have something to finish or because I get an idea that strikes me as neat and funny, and then my interest in writing is back.
Thinking about it, the story of mine that best expresses my attitude toward writing is "Telling Stories to the Sky," published in F&SF and reprinted only once -- in Chinese. There's a wish fulfillment element, because the heroine gets a powerful patron: the North Wind, who lives in a cold and windy palace in the sky. She can visit there in dreams, but she can't stay, because her body back on earth would die; and because the palace -- though very splendid -- is too cold and windy and uncomfortable. She needs her life on earth to stay alive and to get material for her stories -- as well as good meals that aren't cold, the way food in the palace always is.