Maybe the workers moved to where they could make the most money. If equal pay were offered in every location, local workers would start competing against worker

Maybe the workers moved to where they could make the most money. If equal pay were offered in every location, local workers would start competing against workers who would not or could not move. But to some extent, the competition has already concentrated itself locally. Beyond the short-term, people would stop moving to be close to the work so the pay would become more equal across distances.