I feel then people would then complain that they're shipping "incomplete" or "obfuscated" code.

These headers are likely generated from their internal RTL, and somewhat part of the documentation to allow other OSS users to understand the interface. Even if most aren't used by most client drivers, and "just" some internal detail of their firmware/GPU command processing, or even optional and completely unused in current drivers, they may be useful to the community if the host can see and modify them.

Sure, you could argue that should be "split out" from the headers and documented separately, but at this point I'm generally happy for the hardware companies to give the community as much as possible and let them decide what's relevant.