I believe every writer in the world has their own answer to this question. There are no wrong answers, but there are politically incorrect ones.
You not supposed to answer: I'm in it for the money.
Nor are you supposed to admit: I'm in it for the fame.
Face it, some people are. I wish them the best of luck.
Why do I write?
I write because I've discovered I can. I like I'm not confined to an office; although I must admit the companionship would be nice from time to time.
I write because I've always had an active (some might say over-active) imagination. Coming up with plots or characters has never been a problem for me. I don't have a problem meeting deadlines. (no deadline, however, leads to plentiful procrastination problems)
Do I think I'm the best writer in the world? No.
But I like spinning my tales and trying to make them the best I can. I like creating characters who are real. They're funny, sometimes misguided, but always (I hope) very human.
I'm not trying to change the world; I'm not that kind of writer. I want my stories to entertain. To shock? Perhaps. Maybe even elicit the odd snicker. But ultimately, I'd like my readers to close my books with a satisfied sigh.
However, a little bit of fame and fortune wouldn't break my heart.
I'm just saying.
Why do you write?