(AMD isn't even mentionable on this topic; the reason that company exists is to shield Intel from antitrust)
That's a bit unfair to AMD. Ryzen is quite competitive with the latest Core generations. And, on the server side of things, EPYC is so competitive (PCIe 4.0 two years before Intel, up to 64 cores per socket) that Intel had to massively slash the prices on Xeon Scalable with "Cascade Lake Refresh" (see for instance the $4k 6258R quietly superseding the $10k 8280), Ice Lake Xeons—and now W-3300 workstation CPUs vs Threadripper Pro. Thank you AMD!
The issue is that "x86" refers to an architecture which dates back to the 8-bit instructions of the Intel 8088 microprocessor, extended to 16 bits with the 8086, further extended to 32 bits, and eventually extended to 64 bits with the x86-64 instruction set devised by… AMD, at a time when Intel was trying to transition to VLIW Itanium—another instance where AMD existed for a little bit more than "shielding Intel from antitrust".
There's quite some overhead in running x86-64, and therefore much to gain by switching to a simpler and cleaner architecture such as ARM. But it takes some boldness and a full control over both hardware and software to make such a switch. Apple can do it, dragging its users along, as it already did when switching to PowerPC and to Intel.
If Microsoft tried to push for a switch to ARM architecture on the desktop, its customers would just keep buying the same old x86 hardware to run old versions of Windows and the manufacturers would supply indefinitely.
