I write poetry because it gives me a calming yet energising moment to get in touch with my inner thoughts. I write poetry because I love writing poetry. I write poetry to try to sort out how I feel about something. I write poetry because writing a poem is much quicker than writing a novel!
You can go from idea, to first draft, second draft, third draft, fourth draft and finish in the space of a couple of days, when it's going well. Sometimes even, you can get lucky and get it down right, first time, no revision required. That doesn't happen that often though.
I'm always suspicious about people who say they never edit - their work is perfect first time. I know one 'poet' who claims this - he might have short lines, and the end words may rhyme, but there's more to poetry than that. You need rhythm as well, an interesting way with words, something worth saying, and a million other things too, to write poetry well. I find I always improve my work, with every re-draft. Up until that magical point when it works, not just for you, but for other people too.
And maybe that point is the main reason why I write poetry - so that my poetic words will work for other people, to make special connections with other people.
Why do you write poetry?