I dunno, they could have gone to AMD who is on TSMC and have lots of design wins in other proprietary machines where the manufacturer has a lot of say in tweaking the chip (=game consoles).
I think Apple really wanted to unify the Mac and iOS platforms and it would have happened regardless.
If Intel didn't have those problems, Intel would still be ahead of TSMC, and the M1 might have well be behind the equivalent Intel product in terms of performance and efficiency. It is hard to justify a switch to your inhouse architecture under these conditions.
I think Apple really wanted to unify the Mac and iOS platforms and it would have happened regardless.