I would guess that they do know that, but they think for whatever reason that they can't get away with doing the same thing. (Or maybe they'd have to sacrifice something else that they care about - if they started setting higher standards and got 90% of carriers on board, but the other 10% stopped selling Android devices, would that be worth it for them?)

I'm not sure if they're right, but I am pretty confident there are tradeoffs here.