Why would it be an issue for Mexico if the Anglo-American settles were not learning Spanish or practicing "Mexican" culture?

During the early 1820's, nearly 3,500 Mexicans inhabited Texas, and the newly formed government of México wanted to continue inhabiting the state. But, in order for people to be able to live in Texas, they had to agree to obey Mexican laws, practice the culture and its customs, become Mexican citizens, learn Spanish and become catholic. At the end, it would be an issue for México if the Anglo-American settlers were not learning Spanish of practicing Mexican culture because there was a fear that at a moment's notice, the inhabitants would want independence and México did not want states to leave the newly formed Mexican Republic.