I've been thinking about this for awhile. I'm sure we've all got different, completely valid reasons for doing what we do here. But why do you?
I think, for me at least, I can express things musically that I cannot begin to find words for. I find myself limited by words in most cases. Also, on a more superficial level, I love making music, and getting better at it. It's really fun. There is great satisfaction in sitting down to a finished creation, knowing how hard you've worked on it.