https://www.eetimes.com/tsmc-to-keep-supplying-chips-to-huaw...
Same issue here - they’ll switch to ARM for more control. AMD has some good hardware, but they’d just end up switching one outside chip vendor for another. So while a move to AMD would be “safer”, it still wouldn’t offer any more control over their products.
That’s my guess.
It's ultimately an intermediary step. Apple already has the tech for making multi-arch software, it's already a part of the toolkit, and they already design and sell ARM chips in their other product lines. It's not a no-risk scenario, but it's a low risk transition from a company that's managed two architecture migrations before.
The Mach-O object file format supports fat binaries and has run working executables on ARM, SPARC, PA-RISC, PowerPC 32-bit, PowerPC 64-bit, x86 and x86_64 first under NeXT and eventually under Apple. It's what every implementation of Mac OS X, iOS and its derivatives use today and there's nothing stopping Apple from support other architectures down the line other than they probably don't want to or need to. If they decided they wanted to revitalize Mac OS X server and ship them with POWER9 or RISC-V CPUs, they could do that. Not sure why they want to, but it's an option.
If they're going to end a working business relationship with a supplier anyway and they have CPUs that outclass their current supplier in CPU performance (an A13 in a $400 iPhone SE outclasses the Xeons in their $6K Mac Pros in single threaded performance), they might as well go the whole hog, skip the intermediary step of switching suppliers (which might mean signing some kind of multi-year deal during which Intel might start outclassing AMD, so that's not without risk either) and run their own designs through TSMC fabs.
Apple has always been that company that likes to own the whole widget, or as much of it as possible. If they didn't, they might have switched to Windows NT in the late 90s rather than buying NeXT. They don't make everything that goes into a Mac or iPhone, they don't even fab the CPUs in their iPhones, just design them, but they figured out which parts they can control the designs for and which they can source from others and made it work by progressively integrating more of the design work in-house.
Apple is already working with AMD when it comes to dedicated graphics chips, and people have done Hackintoshes with AMD parts for ages... so why go the (risky) ARM route instead?