for me I started out because I was curious about the process of making beer. I started on a Mr Beer kit and made some terrible stuff. (we still drank it) I learned from my mistakes and found a friend who made beer, he taught me what he knew and then I became obsessed with the possibilites.
I still brew for many reason, the least of which is because I enjoy the challenge of trying to match some commercial variety I tried. I really enjoy the creative aspect of making beer and it allows me some time to nerd out. I have taken this hobby pretty far and love sharing it with people. Home brewers are a unique group of people and they are such a fun crew to be a part of.