30 years ago people were making the same argument that MS should have kept DirectX open or else they were going to lose to OpenGL. Look how that's worked out for them.
> Google, who does in fact make money directly from Android sales
They don't though. They have some amount of revenue from it, but it's a loss-making operation.
> In fact there is even a potentially direct analogy between the two platforms: LLM is the top of the stack with GPU on the bottom, just like Advertising is the top of the stack with Mobile on the bottom.
But which layer is the differentiator, and which layer is just commodity? Google gives away Android because it isn't better than iOS and isn't trying to be; "good enough" is fine for their business (if anything, being open is a way to stay relevant where they would otherwise fall behind). They don't give away the ad-tech, nor would they open up e.g. Maps data where they have a competitive advantage.
NVidia has no reason to open up CUDA; they have nothing to gain and a lot to lose by doing so. They make a lot of their money from hardware sales which they would open up to cannibalisation, and CUDA is already the industry standard that everyone builds on and stays compatible with. If there was ever a real competitive threat then that might change, but AMD has a long way to go to get there.