The reason that AMD didn't release their ARM design I think is that they know it is better to only have to compete with Intel than being one of the many ARM designs.
It's like train companies thinking they shouldn't compete with cars because they're in the train business (without realizing they’re actually in the transportation business).
AMD is in the chip business, not the x86 business - and x86 just became a whole lot less relevant for the future.
Apple has the vertical integration to do it properly. Amazon and Microsoft have the server cloud computing to do it server side.
Without proper coordination from Microsoft, third party OEMs, and AMD they'll all fall behind on computing on end devices.
I think that's part of the reason AMD/Intel will be less relevant, the incentives and market moves don't look good for them.