You've expressed some of my own thoughts here.
There's a part of me that wants to "make it big", certainly. But for as long as I can remember, writing, drawing, painting have all been a creative outlet for me. There's something in me that has to come out - it's as if I have this creativity gland and sometimes it pumps out more into my system. When it starts pumping, I have to find a pencil, pen, paintbrush or keyboard and get something down on paper. I have to make something. If I were never allowed to do this, that would be the worst punishment.
I'd love to make it big, be successful doing what I love. Make it a career. That's always an ambition. But first, I do it for me; it's a need.