My only guess is they have a parallel skunkworks working on the same thing, but in a way that they can keep it closed-source - that this was a hedge they think they no longer need, and they are missing the forest for the trees on the benefits of cross-pollination and open source ethos to their business.
IBM and Microsoft made OS/2. The first version worked on 286s and was stable but useless.
The second version worked only on 386s and was quite good, and even had wonderful windows 3.x compatibility. "Better windows than windows!"
At that point Microsoft wanted out of the deal and they wanted to make their newer version of windows, NT, which they did.
IBM now had a competitor to "new" windows and a very compatible version of "old" windows. Microsoft killed OS2 by a variety of ways (including just letting IBM be IBM) but also by making it very difficult for last month's version of OS/2 to run next month's bunch of Windows programs.
To bring this back to the point -- IBM vs Microsoft is akin to AMD vs Nvidia -- where nvidia has the standard that AMD is implementing, and so no matter what if you play in the backward compatibility realm you're always going to be playing catch-up and likely always in a position where winning is exceedingly hard.
As WOPR once said "interesting game; the only way to win is to not play."
For CUDA, it is not just AMD who would need to catch up. Developers also are not necessarily going to target the latest feature set immediately, especially if it only benefits (or requires) new hardware.
I accept the final statement, but that also means AMD for compute is gonna be dead like OS/2. Their stack just will not reach critical mass.
Proton, Wine, and all of the compatibility fixes and drive improvements that the community has made in the last 16 years has been amazing, and every day is another day where you can say that it has never been easier to switch away from Windows.
However, Microsoft has definitely been drinking the IBM koolaid a little to long and has lost the mandate of heaven. I think in the next 7-10 years we will reach a point where there is nothing Windows can do that linux cannot do better and easier without spying on you, and we may be 3-5 years from a "killer app" that is specifically built to be incompatible with Windows just as a big FU to them, possibly in the VR world, possibly in AR, and once that happens maybe, maybe, maybe it will finally actually be the year of the linux desktop.
We already see things like Google abandoning tensorflow support for Windows, because they don't have enough devs using Windows to easily maintain it.
And of course, we have a changing of the guard in terms of a generation of software developers who primarily worked on Windows, because that was the way to do it, starting to retire. Younger devs came up in the Google era where Linux is a first class citizen alongside MacOS.
I think these factors are going to change the face of technology in the coming 15 years, and that's likely to affect how businesses and consumers consume technology, even if they don't understand what's actually running under the hood.