‘Mexican Spanish is permeated by indigenous languages’
https://english.elpais.com/usa/2021-08-13/mexican-spanish-is-permeated-by-indigenous-languages.html
Many Mexicans still feel that Spanish is an imposed language, and do not feel that this is their language
What came to Mexico was Spanish with many dialects influenced by Andalusia and the Caribbean
Because the Habsburgs always had a policy of separating the Indian villages from the Spanish villages. Divide and conquer. Separate them and then each one is in their corner and I can control them better. But in that separation, there was a great respect for their customs, legislation and indigenous ways of life. The Habsburg dynasty respected the separation of Indian villages and they used intermediaries. Documents show that they were Spanish-speaking Indians, in the sense that they spoke both languages. They spoke Zapotec and Spanish, for example.
When the Bourbons ascended the Spanish throne, they totally centralized the administration. They eliminated the separation of indigenous towns and Spanish towns, and of course imposed Spanish. Remember that they had been living together for 200 years, and that the Indians had also adopted Spanish because it was more fluid and faster for them to communicate in Spanish than to communicate in Nahuatl and to look for an interpreter. That was not because of ‘how nice it sounds.’ It was purely for survival.