If you can fill out an ITIN form to pay taxes then you can certainly apply for citizenship. The tax they pay is probably less than one-tenth of what they should. Most of the illegal earnings are paid under the table not to mention half of Mexico is subsidized through electronic transfers from the U.S. "Mexicans in the U.S. send over $60 billion annually to Mexico, reaching a record $64.7 billion in 2024, with the vast majority (around 95-97%) originating from the U.S., making Mexico the largest recipient after India, supporting families, and boosting local economies in poverty-stricken regions."