"People who are really serious about software should make their own hardware. " -- Alan Kay, father of the GUI.
"The Macintosh is not a computer, it is a software program, a concept, that just happens to require its own hardware to run." -- Jerry Pournelle, BYTE Magazine, 1984.
Mac is not just the OS, or the hardware, but a synthesis of hardware and software to do things in ways no other combination can.
If I wanted a computer without MacOS, I'd buy a Dell or build one from generic components. But I want "Mac", so that means I need MacOS, so that means I need Apple hardware to run it.
End of discussion
Brains