This article discusses why the lack of industrial supply chains locally really hurts - the availability of basic parts like custom screws without lead time is exemplary of the problem. The entire chain of production exists in Asia and not in America.

https://www.nytimes.com/2019/01/28/technology/iphones-apple-...

Tariffs and other restraints on trade meant to draw companies in in exchange for “access to the market.”

Although cost reduction was a huge factor.