Crypto currencies are still akin to magic for me and I'm not a hardware engineer by any means, so this is probably a stupid question, but: why doesn't someone create a processing card specifically for mining? Not a GPU but something stripped down to the necessities and running flat out all for the sake of mining.

Granted, a big part of that answer is that it's a limited market when weighed next to the costs of design, prototyping, tooling, production, etc.