>> Apple's business model regarding macOS is to sell as many devices as possible capable of running that operating system.

> I don't agree that this particular trait of macOS makes an implementation at the layer WINE implements (full API+ABI) any harder or easier.

Here is my corroboration. Apple publishes XNU to the world in this repository:

  https://github.com/apple-oss-distributions/xnu

There is no such publication of the GUI frameworks required by macOS programs.

> I do think there is an argument to be made that Win32 was more straightforward ...

I did not make that argument. Instead, the position I hold regarding Windows is:

  ... an independently derived emulation layer is
  possible (not easy, just possible) ...

When an organizational goal is to sell devices, instead of operating system licenses, there is no need to engineer portability within the OS as the target hardware is well-known. This is a luxury MS-Windows never had, as its goal has been to run on as many disparate devices as plausible. Thus the "intrinsic portability" I referenced.

In fact, you have made my point for me:

> ... while slow change is useful, backwards compatibility expands the Win32 API surface area, since each API also needs to continue to support every way it was ever wrongly used.