I buy manga because
- I like to see them in the shelves.
- I like to collect them.
- I like the feeling of waiting for the recently bought manga to arrive...
I don't have anything else to use my spare money for, so why not?
EDIT: Yeah, I know you were talking about anime but it was an interesting subject so I thought I'd respond ;o
You could probably just look those all up.
EDIT: Aw, dicks, my cat just tore up my camera >->
I'll try to use my phone or webcam, whichever turns out to have better quality.
Plus, there is the awesome feeling of opening a manga up (also, does your manga have some sort of unique scent when you open up a new one?).