Short and simple reason:

Admins.

We need the ability to run our own servers, otherwise the community will fade away into nothingness. This is rather sad, but true. Already, because of the people using aimbots and other unscrupulous (I think that word has quite a bit of awesome in it) things, the player count is dying out.

That alone has the potential to be a total game changer in MP, and might allow a community to stand. However, it'll never happen. They'll never turn the server files public.

Yeah, it's unlikely that EA will relinquish their vice-like monopolized grip on the servers...

Admins. They're like referees. Some good, some bad, but all have a purpose. To REGULATE THE GAME.