CUDA is their moat and their drivers do add significant value, seemingly more than AMD. So it's reasonable to expect that these won't be open sourced any time soon. Honestly I'm surprised why people expect them to just open source core IP like this.
I think a lot of folks are hoping to fix bugs in the Linux implementations for things like power scaling.
In cases like CUDA or OGL, it seems that the the kernel compilers are part of the driver package, which further confuses the discussion.