Insanity motivates me. My mental stability deteriorates when I don't write (depression mostly) so I write a little every day just to keep the demons away. I'm pretty prolific because of this (6 novels in three years) but I don't seek publication or pay (though I do put them up for free on Smashwords and Kindle). Therapy is the value I get back from writing.
I'm almost done with a draft of number 7 now and 8 and 9 are in the outlining stages. And all this derives from insisting on at least 1,000 words a day, even if it's dreck. I just deleted 5,000 words from my draft without a care the other day. A thousand words really adds up even after discarding a hefty percentage of it.