Mary Jordan and Kevin Sullivan write Trade Brings Riches, but Not to Mexico's Poor. They blame NAFTA, but admit

Mexico's weak public education system condemns workers to low salaries in a global economy where skills count. Decades of systemic government corruption have robbed the poorest of everything from high school scholarships to subsidized milk. The broken banking system hands out little credit -- people without the cash to buy a house or start a small business must often do without.

Mexico's inability to enforce the rule of law also discourages the investment needed to create jobs.