I definitely write poetry more often than anything else, though I do write other things sometimes.
To be honest I'm not sure why I write poetry more than any other style -- maybe it's because other styles tend to require more forethought or time -- I write in a single sitting, most of the time, and I write straight from the gut with no real idea of where the piece is headed. I know you can do that with prose, but I tend to start a prose piece and then walk away from it, leaving it unfinished. Perhaps it's just that writing poetry requires less patience (for me) than prose does!
I'm very curious what the "dick kick" responses were, will you enlighten me?
It's not exactly insufficient motivation to write, though. I have plenty of motivation to write, I just don't like revisiting things -- I'm fickle! I also have a personality disorder that contributes because I find it difficult to find the 'pace' where I left it, which means if I return at a later date, I'm likely to completely jump moods, which is very offputting (to say the least).
As for planning, I can plan, I just don't like to. I suspect I get 'bored' with things when I know where they're going, which contributes to not finishing things. My last NaNo attempt was quite well planned out into a notebook! (But yes, it's still unfinished. )
Really though, I'm still giggling over the dick kick. I promise not to tell your dirty little secret to anyone!
I do do that sometimes, but mostly it just works better for me to concentrate mainly on poetry. Also, editing is revisiting, too. Fickle, I tell you!
Another possible reason is that mostly I write short moments rather than more in-depth stories. Again, can be achieved through prose, but poetry is more often how it appears.
Please don't think from this though that I only write prose when I have to -- for me they're just very different campsites, and I visit them for different reasons. I might camp more often beside a river, but I can still appreciate the beauty and fun of camping on the beach, too.