While I know Apple isn't exactly stopping this sort of knowledge discovery and distribution, I don't know why they aren't helping it, given that any increased demand of their hardware would just result in more hardware sales
This is the same mechanism by which Microsoft has eliminated the competition for Microsoft Office, which used undocumented Windows APIs so that the products of any other vendor could not keep up with it, especially after the launch of any new Windows version.
Now one can find some more complete documentation for the Apple CPUs as the result of reverse engineering work done by various people, but after each introduction of a new Apple CPU model the reverse engineering work may need to be done again.
Examples:
I'm not here to defend other anti-competitive practices by Apple but as far as just their CPUs go, there are none in that area.
AMD: https://gpuopen.com/amd-gpu-architecture-programming-documen...
Intel: https://www.intel.com/content/www/us/en/docs/graphics-for-li...
These peripherals are accessed with memory-mapped IO using the same instructions any other program uses.
Documentation about ARM64 assembly shouldn't and doesn't contain specific peripheral access info. ISA docs contain info common to all CPUs implementing the spec.
They clearly are helping. Perhaps you've not noticed?
In contrast, AMD and Intel publish GPU documentation.
The original post's point was that by being more open they would encourage more software to be built for their platform. That would create more demand for their products from consumers.