I voted other because some of the options are true for me, and some others were not there.
I GM because I love making up the stories, NPCs and then seeing them interact with the PCs. I enjoy the collaborative story telling that takes place when you describe a situation, and the characters react to it in the most unexpected way, then I have to somehow describe what happens next.
Also, it is a great excuse to spend time with friends.
On the rare occasions I get to play as a PC, I enjoy creating the character, watch it evolve, and also the puzzle solving.