They design their own chips in-house, they are moving to use them across their full stack, they are already TSMC's #1 customer by a wide margin, and they could literally build a 3nm fab with 40k wafers per month with less than 10% of the liquid cash they have on hand ($5b for the node and $15b for the fab). And they are the type of company who brings everything possible in-house, and the type of company who looks at a single-source monopoly like TSMC as a business risk. Fabs are literally the last part of their hardware/software stack that they don't control and that another company could potentially leverage them over.
Right now there is no alternative to TSMC, people literally pre-eulogize NVIDIA Ampere and other products simply because they're on Samsung instead of TSMC. How do you think that looks to a company like Apple, that they are completely dependent on this company for node tech and subject to increasing competition for wafers as everybody else realizes there is no alternative and piles in too?
https://www.extremetech.com/computing/272096-3nm-process-nod...
There's also TI's site in Freising which is a notable fab producing analogue parts.
It would also be nice to have some capable foundries in Europe, like STM or Infineon. Just in case.