Everyone has their own reason to pick up the pen.
I have always loved reading and writing since the time I was able to read/write on my own. My reasons back then were simple. It was something to do, it made me feel smart. But now those reasons have evolved. Ever since I was little, people liked reading what I wrote. I remember once in first grade my teacher wanted me to read a story I wrote to the fourth-grade class. And in a school where there was only one hallway and one classroom for each grade, that was a big deal. Then middle school rolled around, and my writing took a more serious role in my life. It became a coping mechanism.
When I was during the worst stages of my depression, my writing was one of the only things that got me through. It was a way for me to find emotional release in a healthy way, and at the time it was probably the only healthy coping skill I knew. I had stopped writing as many short stories, but when it came to my day-to-day events, I wrote about everything. I kept (and still keep) a detailed journal, I had a my own personal poem book for me to fill in. Most of my classmates didn't understand, probably because I come from a town where you get more respect for shoving the barrel of a gun in someone's face than you do for coming up with some intellectually challenging pieces of literature. But that was fine, I didn't need them to understand.
Once I got into high school I started taking my writing seriously. I still kept my creativity, only now I learned how to make it structured. Chronological, it made more sense now. Around this time was when I met the most influential man in my life, my old English teacher Mr. Sundrham. He taught me to appreciate literature, both when writing and reading. He is the one who really fine-tuned my skills. I learned how to properly use metaphors in ways that make the hairs on your arms stand on end, he taught me how to dig deeper into my imagination than I thought was possible.
But it seems that is merely my literary transformation, I didn't answer your question Why do I write, you ask? Its an amazing outlet. Its the only way you can say exactly what you want with no reactions or repercussions, because you can just flick a bic and watch those disrespectful thoughts go up in smoke. With a combination of 26 letters you can create a whole new world, a whole new dimension. With just a combination of 26 letters you can make a person cry, and then dry their tears with the next page. You influence emotion. You can create what everyone told you was impossible. There are literally endless possibilities, and if that doesn't excite you in some way, then you probably shouldn't write.