Forecasts are that China wants to forcibly reclaim Taiwan much sooner than anticipated. And maybe they are confident that China wouldn't retaliate against them but surely that's not a risk worth taking.
Foxconn has been asked to ramp up production in India but not sure if you would call it a success or not.
If I'm running a PCB assembly line and my primary supplier of surface mount capacitors is the only guy within 50 miles, where do I get replacements from if something happens like there's a fire in his factory and it goes offline? In Shenzhen you go to the next guy down the street who's selling the exact same part.
So instead of being down for three days while finding a way to get an additional supplies airlifted in you can have probably have another supplier up and going before you run out of what's left in the lean manufacturing pipeline.
Before making the move to any labor market concerns like those have to be addressed or at least the risks mitigated. That takes time and costs serious money. As the SMT industry ramps up in more locations it'll be easier to diversify assembly locations.
Shenzen is like that. Everything you need for electronics manufacturing of nearly anything is located in the city. This means that if part of the supply chain is disrupted in normal times, you could go get the same part from somewhere else not far away.
Today, the United States auto manufacturing isn't that way... and frankly it isn't even fair to say "United States auto manufacturing" - https://cimg3.ibsrv.net/gimg/www.corvetteforum.com-vbulletin...
So, here's the problem that Anyone building an iPhone would have - where do you get the capacitors on the board from? how much lead time do you need to keep the supply going? What happens if the supplier isn't able to send them? How big of an industrial base do you need to make all the parts and how distributed is that industrial base?
Possibly because they've got a former CFO running the company which causes a myopic view towards profit rather than interesting hardware development. The age of apple dropping new product idea after new product idea is long past.
A finance-oriented CEO that is concerned with profits should be more concerned with instability and risk, compared to a product oriented CEO who would be concerned about the next hot thing.