Forgive me if the question is wrong but I must say I usually need to write. I must. I have to.
I don't have speciel reasons.. I wouldn't like others to read it and to show my feelings to them but of course I am happy if someone says it's worth and he reads it.
I write because I need to.
Maybe it isn't an answer to this question but for me this is the only answer.

But what about you guys and friends?
Why do you write?
Why do you need to write? (If you feel the same way as me.)