The biggest reasons are the loss of domestic experience curves [1] to other countries when we shifted to a service based economy. The second is the hyper politicized process of even creating a factory, let alone operating one, even when you have the direct backing of the executive branch [2].
The other one (allegedly) is the idea that the local labor workforce won't want to do any of the hard/dirty jobs or can't do them cost effectively, often because 1 and 2 but other reasons. So there are higher initial costs for automation.
But otherwise there are plenty of good reasons to operate production domestically once the technical and political environment supports such a thing. Which might happen in the future, although few mainstream parties seem to actually want that to happen without their idealized or prior worldview being appeased.
[1] https://en.wikipedia.org/wiki/Experience_curve_effects
[2] https://www.bloomberg.com/news/features/2019-02-06/inside-wi...
https://www.theguardian.com/business/economics-blog/2014/nov...
This is an old pattern that's just getting more efficient and China's able to sell to it's own markets. Freeing up more human and financial capital for China to do their own R&D/entrepreneurship.