Apple don't move to China to save money, they moved to China in order to meet high demand. There was simply nowhere else that could produce the volume. And technically, Foxconn is a Taiwanese company, but that's not an important detail. Point is, only Chinese/Taiwanese contract manufacturers could give Apple the volume they needed.

I really wish you could talk to some more manufacturing types -- there are many on this site. A lot of things at scale can't be done anywhere except in China.

Now, you can argue that's just about "saving money", because Apple should have built its own automated ports and infrastructure and commodity trading hubs and paid to relocate workers to create a bespoke manufacturing center somewhere else -- but subject to realistic constraints, there was China and no second option to produce iPhones at scale.