None, all, or any of the above.
Composition is simply "creating" or "putting together". On some rudimentary level, it may just be part of a biological need to create something that "goes beyond" the creator. Not unlike humanitiy's need to precreate in order to continue the species we build buildings, and monuments, and create social systems, and works of art, and so on. It would be nice if everything were done for completely altruistic reasons but certainly, any of these things can be done as much for personal gain as societal gain. I suppose, in a free society, it's up to each person to discover what drives them to create. Actually, I take that back. For some, it really doesn't matter why, it's that they *must*, so they do.