"Leave the why for psychologists. It's enough to know you want to write. Write.
"I write because I am crazy, schizophrenic, and I know it and accept it and I have to do something with it other than go to the loony bin.
"I write because there are stories that people have forgotten to tell, because I am trying to stand up in my life. I write because to form a word with your lips and tongue or think a thing and then dare to write it down so you can never take it back is the most powerful thing I know. I am trying to come alive, to find the distances in my own recesses and bring them forward and give them color and form."
- Natalie Goldberg, Writing Down the Bones
"A writer is not so much someone who has something to say as he is someone who has found a process that will bring about new things he would not have thought of if he had not started to say them. That is, he does not draw on a reservoir; instead, he engages in an activity that brings to him a whole succession of unforeseen stories, poems, essays, plays, laws, philosophies, religions…"
- William Stafford
I write because I can't not write. I am as compelled to put words to paper as salmon are to spawning upstream. I write not because I try to put the djinn back in the bottle, but because I must let him out. The ID must be unleashed and allowed to roam free, else the EGO will bind him forever in some forgotten corner, ignored and undone.
- TJPontz
Now then. Why do YOU write? Hmmm?
T J Pontz 
I write to tell my story to myself, to quiet the ’round and ’round head chatter, to make sense of and give meaning to my experience. If that meaning can be conveyed to another, if it can bring an “aha” or some healing, then I have done my work.
I write because there isn’t enough room in my head for all that’s going on in there. I have to give the voices structure, I have to give the scenes a place to live, and I have to give ideas a chance to stand up on their own. I write because I have to.