Because in the absence of that physical connection you begin to accumulate a social and economic debt that will eventually come due, because sooner or later that 80% working in the service economy will come for the remaining 15-20%. Domestic manufacturing made possible by some degree of anti-dumping/tariffs would at least create a more balanced distribution of this wealth.

Globalist trade promoters are just short-term wishful / magical thinkers. It's magical thinking that you can create this social and economic imbalance via outsourcing it to the other side of the globe, without consequences over the long run. It's wishful thinking that there are enough upper middle class jobs / lifestyle for everyone that took Calculus.