They probably don't want to sell those chips for Android to keep their competitive advantage, and the PC market is probably too small to be worth the investment compared to the iOS market.
Intel is currently worth 1/5 of Apple 1 Trillion. I guess they may want to grow by 20%, but not at the price of exclusivity oof the 1bn device market chip exclusivity - however I'm not sure anyone has an iphone because it's the best benchmark performing phone. What's next, overclocking, liquid-chilled phones ? (after looking at it for fun, yes, it does seem to exist, just look up liquid cooling gaming phone ).
That 20% includes Fab, which is more than half of Intel's value. Apple partnering with TSMC meant even if they could get all of Intel's market it would still only growth of 10%. Apple would be much better if they spend time designing chips for their own macOS and sell more Macs.
