So many economists have rationalized the benefits of free trade as being that the country who can make things most efficiently and with the best quality will succeed, but they ignore what goes into "efficiency". But worker safety protections (especially from litigation risk), higher wages, and better time off are all significant sources of inefficiency, from a production standpoint.
The market devotee acknowledges that the market solution to worker protections is unionization and job-shopping, but it's nearly guaranteed to put enough pressure on corporations to offshore as soon as possible. Unions help wages for those jobs which stay, but guarantee there aren't that many left. Free trade with places like China and Mexico is stacking the deck against American labor.
Conservatives have long used unions as a scapegoat for this problem, but it doesn't explain why it's more often the case that a corporation offshores operations instead of moving operations to a state without government mandated unions. There is some truth to their argument, but I don't think they understand that basic safety protections, natural market forces, and potential litigation all contribute to a significantly more costly American worker than one abroad, even if they aren't in a union.
I think that one of the central reasons this has been happening is that the American ruling class has been insulated in their ivory towers and Ivy League schools for too long. They're genuinely more concerned with "saving the world" than creating a cohesive, prosperous society. It explains why so many lives and money is used to intervene in countries on the other side of the planet, why immigration from 3rd world countries is heavily promoted despite fierce resistance from the lower class, and why they have all but abandoned the idea of low-skilled labor becoming more valuable.