Ha, good timing! I just finished pondering that very question and posted in my journal about it. Fear of being forgotten when I'm gone is a big motivator for me. Can I be passionate about fear? Ahaha, I sound so melodramatic! (I'm not really!)

I do them anyway, because they need to be done.
Actually, that pretty much sums it up for me! I feel compelled to do them.
Making a comic means hours of drudge work. I think you either need passion out the wazoo to sustain you or you need to view it as a job in order to slog your way through to completion. I can honestly say I look at making a comic as if it is doing dishes, only in the case of the comic I don't have a machine that automates most of the work for me so it is more like doing dishes by hand. =p But, like having all my dishes done, I come out of it with a sense of satisfaction and I feel pretty proud of myself. (Maybe if I didn't have to do ALL the parts of making a comic myself, if I could just do the bits I consider 'fun', I would feel more passionate; as it is the drudgery kills a lot of the enjoyment.)

But if I don't feel a surge of emotion or joy while I'm writing a poem, I won't finish it. I create for pleasure, not out of necessity.
Would you say that this means you would be happiest keeping your poetry writing as a hobby rather than a full-time job?