They enjoy performing and want to perform original songs. Some people love to perform, but they aren’t into performing cover songs. So, they write their own material. Often these people are trying to define themselves as performers.
Writing is therapy. I’ve often written simply because it feels good to bleed on paper and get it all out. In most of those instances, I had no intention of trying to get someone to record the song or even for anyone else to hear it. I just wanted to get my stuff off my chest.
They want to hear others sing their songs. These are the writers working toward the goal of hearing artists record their songs and make money from them. These writers have to work differently, because they are trying to speculate what an artist might say and to become a “voice” for that artist.
They simply love the process of writing. These writers just like to write. So they do. Not for anyone else. Not to get something worked out. Just for the satisfaction of having written.
Why do you write? Discovering your true motivation for writing can help you figure out how and what to write. If you write for yourself, you write differently than if you are writing for others to perform. Writing for therapy is completely different than just writing to write. Many of us write for all of these reasons at one time or another. Give it some thought. Figure out what causes you to write songs and you’re onto something interesting.