[HHad3]

In addition to the points already mentioned, a good bit of Apple's software depends on Intel-proprietary features, e.g. QuickSync for video encoding. So far, no macOS system ever shipped with an AMD CPU, and porting the OS and user-mode application stack is not trivial.

[wmf]

There must be Macs like the iMac Pro and Mac Pro that don't have Quick Sync.

[tachion]

You will find people using Hackintosh machines with AMD cpu's just fine (as much as fine it is possible for a Hackintosh, that is).