Yes people can and do move from Mexico to the Midwest all the time.
Why do you think Mexican laborers should get paid less for building your car then someone in Detroit? Part of the goal of NAFTA is to help stabilize the economy of Mexico and help longterm reduce the severe violence in parts of the country.
I am not Mexican but it toke my family 14 years to be able to move to the US from Palestine, although my grandparents and uncles have been here since the 80s. It really isn't hard.
A company doesn't need to move everything, they can just literally build a new factory or rent one else where, not only that they would even get tax breaks as incentives for moving.
Borders enforce the huge discrimination in pay between TJ and San Diego. Even though the same companies work on both sides of the border.
> The North American Free Trade Agreement (NAFTA) created special economic and trade relationships for the United States, Canada and Mexico. The TN nonimmigrant classification permits qualified Canadian and Mexican citizens to seek temporary entry into the United States to engage in business activities at a professional level.
> Among the types of professionals who are eligible to seek admission as TN nonimmigrants are accountants, engineers, lawyers, pharmacists, scientists, and teachers.
https://www.uscis.gov/working-in-the-united-states/temporary...