Avoiding environmental regulation was one reason to move factories to China, avoiding unions and high wages was another.
But the local communities weren't demanding that their factories be moved overseas so they could have a clean if impoverished towns. Your entire causality is completely backwards.
Free trade / globalism was the larger "true" move, and yes getting away from unions and high wages to maximize profits was a big part.
Corporations made a change from valuing stakeholder value (employees, communities, customers, suppliers, the nation) to pure shareholder value (profits over everything else, despite the long term result that profits by any and all means hurts all stakeholders and eventually can cannibalize the company unless you have monopolistic moats).
Was the New Yorker crowd clinking glasses together talking about how good it was to get the dirty steel mills out of the country? Sure maybe but this argument never resonated with anyone on the ground.
Were companies actively moving factories offshore so they could be dirtier because they didn't have to comply with American environmental laws? Absolutely.