Wow you got that backwards. They don’t do any of that for the sake of Nouveau or Vulkan or Wayland or whatever. They don’t care what people use their open scraps for.
They open up the minimum they can get away with because it’s ultimately meaningless — their proprietary stuff is still hidden away and it’s not like you can use the parts they open with anything else.
This, btw, applies to AMD and Intel too. The only choice you get with proprietary hardware that you have to use (like GPUs) is whose dick you want to suck. They’re not your friend and they won’t let community pressure then into decisions.