It's just guess, but it very much possible Apple simply can't publish any documentation because even they use a lot of 3rd-party IP under NDA. Also publishing documentation officially make patents attack easier.

I not into defending Apple, but there are plenty of reasons why they're okay with Asahi team reverse engineering their hardware, but won't invest any money into making it more open. After all they earn a lot from subscription services and Linux users wont pay for them.