Because it's not a notebook chip? 105W is... a little toasty.

Yeah, I don't think you need downvoted into oblivion for not knowing, but AMD mobile APUs are also not anywhere near this level. The top-end Ryzen 7 3780U is a 4-core multi-threaded part, using Zen+ rather than Zen 2, and the older Vega graphics. (And that's only available in a Surface laptop.)

https://en.wikipedia.org/wiki/List_of_AMD_accelerated_proces...

They're Intel based mobile systems. The 3950X is a desktop class AMD CPU.

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.

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

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).

Desktop chip and even AMD recommends water cooling it.