The OEM is selling a tradable, so you would expect companies to already search the world for the cheapest version and be buying that, as there is effectively a

The OEM is selling a tradable, so you would expect companies to already search the world for the cheapest version and be buying that, as there is effectively a single global market. Labor, historically, has not been so mobile. There is not a single market for labor, there are many different markets. And in each market, the company pays the prevailing market wage. For that reason, when someone moves from market A to market B, their wages are adjusted up or down based on the cost of labor in those markets.