Why did the wage gap between Mexico and the United States not shrink significantly under NAFTA?

The wage gap between Mexico and the United States did not shrink significantly under the North American Free Trade Agreement (NAFTA) primarily due to strict immigration restrictions that prevented the free movement of labor between the signatory countries.1

Additionally, the expected convergence of wages was hindered by a lack of infrastructure in Mexico, which discouraged many U.S. and Canadian firms from making the direct investments necessary to stimulate broader economic development and wage growth within the country. While the agreement facilitated a dramatic increase in Mexican exports and the expansion of maquiladora manufacturing plants, these factors did not translate into a significant rise in per capita income or a narrowing of the wage disparity between the nations.123