How much time/money do you think it takes to implement gamepad support compared to the rest of a game project's development? Maybe a couple of days with an SDK?
Sometimes, the producer doesn't even consider porting a particular game to a particular platform until the platform has gamepad support. In such a case, it might take even longer to get the port up and running, as the port team would have to familiarize itself with the new platform. Ouya and Shield hitting store shelves and the "Gooya" announcement are likely to change this.