It is a lot of work. But having not really done it myself would they not already have most of this? At least one would hope they would?

They need to have that sort of documentation internally anyway for their macOS devs to work on it, right?

And good luck convincing the team of lawyers to groom tens of thousands of pages of internal confidential documentation and source code and prune what can be release to the public and what stays classified as a competitive advantage.

As lawyers usually play it safe (they're paid to defend the company) they'll tell you to keep everything internal internal, since Apple makes money selling finished products and services, not selling discreet chips to OEMs who's functionality needs to be explained to third parties.

Yeah, in the form of “here’s some excel spreadsheets from the hardware team and half-generated C sources from the validation team, just ask them for more info”.