But Intel don't manufacture any ARM mobile SoCs that would be suitable for iPhones and iPads? It's not just a case of "upload A18 design, press print". It is at least a year or two of getting the processes up and running and validated.
So if TSMC went down tomorrow, you can't exactly phone Intel up and say "hi we need 1billion m-series chips a year, starting in a few weeks?"
If they owned it they could start doing that in the background.