Why am I writing?

After scurrying around to get the most-recently-polished version of my book to the agent who requested it, I'm now a computer potato, sitting on my butt. I could be working on the second book in the series. I could be finishing up the vampire romance, which is my first attempt at an actual one hero/one heroine, happy ending short story. I could be starting a new book with some of the ideas that have been flying through my brain. But no. I sit. A friend recently asked me if I write because I like it, or only because I want to sell something. I immediately said it write because I like it, and that's true, but it's not the whole truth. It's the same as my singing career. I have a great voice and I love to sing. So, why aren't I singing in the car? In the shower? No audience. All the years I performed (and complained about it, what an asshole I can be) I recognized that half the joy of singing for me was the appreciation of the listeners. Why should I be surprised that I'm the same with my writing? When someone tells me I write well, and/or that they like my story, I become super motivated. Fingers flying on the keyboard, butt on the chair til the wee hours. But in the lulls, I do nothing. If a tree falls in the woods and no one hears it...