The Mexican government was pressured by the U.S. government.
The best explanation for why the Mexican government allowed Anglo-American settlers to bring enslaved people to Texas is that slavery was legal in Mexico. The Mexican government did not have a specific position on slavery and thus deemed it legal within its territory. This allowed the Anglo-American settlers, who were primarily from the Southern United States, to bring their enslaved labor force with them to Texas. Slavery played a significant role in the economy and culture of the Southern states, and the Mexican government, eager for Anglo-American settlers to buy land in Texas and promote economic development, did not impose any restrictions on slave ownership.
The correct answer is: The Mexican government had no position on slavery.