Console developers have certain rules to adherd to when creating games on consoles. As far as I understood it, some of these rules make fully programmable buttons allot harder to do, it makes it harder for a game to pass the Quality Assurance process. That is no excuse of course, but it explains why devolopers think its not a relativly simple change.
I do believe in accessibility for everyone. I don't know if we will ever achief it but I do think it will be possible. There are some accommodations that interfere with another persons accommodations but these situations are very rare and only come up during multiplayer (because otherwise you can just switch of the accommodations this particular player doesn't need), and even than, solutions have allready been thought of (multible headphone sets, multible screen even).
In theory every game could be made accessible if the information the screen and sound would outpute, would also be availabe in other ways, accommodated for a particular player, and if one of the availabe input methods would be suited for that particular player, plus the game should be downscalable to a difficulty (or/and speed) that destroys any "test element" and makes the game more of a toy than an actuall game.
If you cover those three area's, every game is accessible in theory (even to babies or people with multible severe disablities). In practice, this is very very hard though and a good start would just be those easy to fix things. like, indeed, programmable buttons for every game.