I completely agree with that, but since everything else in my life seems to revolve around some type of schedule, it would be nice if I could get writing time squeezed in there on a regular basis. It's one of those "square peg in a round hole" things, I think. However, I am nearing retirement, so I am looking forward to change (for the better, I hope).
Inspiration, for me. Most of my stories stem from my dreams/nightmares, and whether they're epic and beautiful or a disturbing mindfudge, they're always vivid.
For me, it's not one thing, more of a self perpetuating cycle of: > inspiration > plot ideas > emotion > love of writing