I believe it's the perspective. In the United States and Mexico it's thought that meat fills the plate. That it's what gives you the strength to build muscle. Meat is found in the majority of fast food restaurants and plays a huge role in the main dishes in Mexico. While yes, in Mexico they have their Mexican rice and black beans. It's not viewed as the main dish but rather the sides of your meal. This is unless you get gorditas with black beans and cheese. Regardless, it's hard being vegetarian in Mexico, especially vegan when there are so many problems with whether the vegetables have been irrigated with clean water. As for the United States, meat is just tastier and more heavily advertised in commercials.