Personally I'd be interested to see what would happen if Sony/MS did what they could to make keyboard/mouse experience as good as possible on their consoles (I'm writing from a position of ignorance on the state of mouse/keys with current consoles) and encouraged developers to offer a choice in inputs, so that the locked-down machines can become the place for highest confidence in no/low cheaters. If other people want to pay through the nose to go beyond what consoles offer on the detail/resolution/framerate trifecta then I'm sure they could do so, but I really don't see how you lock down an open platform. That challenge has been going for decades.
All major consoles support keyboard & mouse or similar.
The problem is more the audience. Console players generally expect to be able to just connect the console to the TV, sit on the sofa and play with the official controller. That’s all the game are required to support to be published on the platform.
Even if you were willing to play at a desk, you’d be matchmaking into a special (and small) mouse pool on the console game. Anyone willing to go through so much faff will accept the extra annoyances of a PC, even with kernel anti cheat.
If the alternative is losing the entire Xbox market? Money makes people and companies do funny things.