Second, keyboard and mouse hasn't been used for consoles because it goes against the design of consoles. Keyboards and mouse are clunky, they require a dedicated space of their own. They're not great for using on a couch or sitting back in a chair, basically anywhere without a desk or something to rest them on. Joypads don't have that problem.
There have been some games before that let you use a Keyboard, but by and large most are designed around a set amount of buttons on a controller.