They long to comfort, inspire, challenge, and emotionally move their listeners. Some songwriters use their art as self-therapy. You can always tell what they are going through by examining their most recent lyrics. Their current mood is reflected in the tempo and key of their latest song. Sometimes it can be almost painfully revealing and personal.
Some songwriters write for the sheer joy of creation.
To start with a blank sheet of paper, and create something that didn't exist before still amazes them. Maybe you've seen a little of yourself in most of these reasons for writing. They can all play a part in your life as an artist. Personally, we love working with writers who have a strong sense of purpose behind what they do. They have thought through their reasons for writing and performing, and know where they want to go and what they want to accomplish.