I dunno, I think it's one big marketing exercise with a future tax break sweetener. I don't think it makes business sense in any other way but you cant tell Trump supporters that one!
What Tim Cook is talking about in regards to lack of skills is not just basic assembly but more technical fabrication jobs. China not only has these guys, but has them in droves. It's not like they don't exist in the USA rather they don't exist in the volume needed to do that scale that Apple would like. It's not just about wages, it's about ability and scale.
https://9to5mac.com/2016/12/29/apple-iphone-city-china-manufacturing-foxconn/
When Apple’s sales took off after the introduction of the iPod in 2001, Foxconn had the heft and expertise to meet the demand that accompanied each hit product. Foxconn’s factories could quickly produce prototypes, increase production and, during peak periods, hire hundreds of thousands of workers.
This has happened because countries tend to specialise in certain types of businesses. For example, no one cries when you say it's easier to get a certain type of investment banker from NY or London than its would be in China. That is because the NY and London specialise in that type of business and cultivate workers accordingly. Large scale manufacturing has disappeared from the USA so the expertise has also gone. It will take time to ramp up, and who will do that?
One of the reasons Apple doesn't do it is because, frankly Apple haven't been into direct manufacturing for a very long time (if ever?). The economic reasons are simple. If Foxconn own the factory they can maximise it's output producing goods for other companies in the times that Apple products are not needed so much. If Apple owns the plant it has to have 100% utilisation to make sense. Apple isn't going to start making stuff for other companies so it's kind of a waste of time and costly to directly own these factories. It's pretty much JIT (Just In Time) manufacturing for Apple, using things as they need them. One of the reasons the Japanese companies have had a hard time competing with S.Korea, China and other Asian countries is that Japanese companies like Sony have traditionally owned lots of factories and its killing them. Over capacity and underutilisation is killing them. Apple have avoided that mess.
The last point I want to make and the most important is that the cost of living in China and the USA are way different for most people. Increased credit in the US economy has meant that US property prices are expensive relative to countries like China. Therefore salaries need to be more to pay workers. So when people say "oh its because you can get away with paying cheap wages in China". Well of course! They aren't paying 500k for a basic home in a Chinese village like US citizens have to!
So America is a victim of its own success (or Credit and Interest Rate policies!). It HAS to pursue higher value service industries and high tech equipment making because it's created a society that is too expensive to have basic factory work. Unless the factories are specialised (say Shinola watches or bikes etc..) it's never going to be as cost effective as manufacturing in China or Vietnam etc.. It's all ******** really. But the politicians won't (or cant even explain the economics) behind why things are the way they are. And who can blame them? They need the US citizens vote and will tell them any old ******** to get it.