The distance between Mexico and America is about 2000 km, that's the distance from the city center. Of course if they are near the border, then they will be closer for access to Mexico than access to downtown America. Of course America has quality medical services, but access to these areas certainly makes people prefer to apply for passports to seek treatment in neighboring countries. As a rule, medical services depend on who comes for treatment. It is likely that Americans will bring suitcases of money with them so that they can get a better place. Have you ever found a class A service system, Class B, and so on. It shows that there are differences in services for those who seek treatment. Habits that get class A service will get a VIP room.
I am not sure if the people are traveling 2000 KM and saving some money
Its better to have a hospital near your home and so that you can go for the emergency check up when needed.
Depends on where you live though, isn't it? I mean if you live in Seattle, going to Mexico makes no sense, Canada is better for that case, but if you live in Texas, then I am sure there must be some closer, the distance between America and Mexico is nothing, with one step you go from USA to Mexico, it's a land border. So all in all from your house to a hospital in Mexico may take less than you may think.
And if I was Mexico, I would have built a ton of hospitals near the border to make sure Americans can come and go as they wish, instead of spending 5k on American hospital, they would spend 500 in Mexico, and that would be a lot there. It's a good business venture that would help everyone but the pharma industry in the USA.