There are several reasons people write. It's fun, they're hoping to get rich (and don't understand the reality of writing and publishing), they've got lots of time and nothing else to do.
Well, ok, I doubt that last one would come up. I know my time gets filled pretty quickly with necessary tasks (and fun tasks).
So why do I write? I guess like many authors who decided to start writing as a child I simply can't NOT write. I tried once. It didn't work. There are stories to be told and I'm the lucky one who has access to these stories. I guess that means that even if I never get published I will still write, because the stories want to be told. Even if it's just to me. And I love editing. I love changing around words on a page. I love seeing them join together in new ways, better than before.
And despite the amount of books out there and the number I've read there are still stories I'd like to see that no one else is writing. For quite some time while shelving chick lits I've read the descriptions on the backs of them, wanting to find one that I'd actually enjoy. I've even skimmed a few and gotten frustrated as the main character is similar to me in some ways but always has a high fashion sense (which I don't), and a high profile job (which I don't), and sleeps with every man who offers (which I don't). So to aleviate my desire to read a chick lit that I can relate to I wrote one. Which, now that it's finished, I've discovered is harder to sell than I thought. I doubt this is because there are no other tom boy style women who work retail and who don't think casual affairs lead to worthwhile relationships. But the publishing industry is set up to cater to those genres already selling. When something new comes along they're afraid of it because "how will it sell?". Which ulitmately is a valid point.
But I digress. I write because I like to. I write because I feel compelled to. And I write because I know no one else will write the stories I want to tell.