Disclaimer: This is my experience of living in the United States as a Mexican. So I can't confirm the preferences of people in other countries. Besides, I won't count mexican american, who is of Mexican descent recently, because they may be used to dishes that most non-Mexicans are wary of. Finally, these are just common; I won't touch more obscure things, such as grasshoppers.

Moore must be the more extreme one. This is a classic mole stewed chicken:

Sometimes it is made into meatloaf.

This often belongs to the category of love/hate. Personally, I like it very much, but its sauce (if you can say so) is different from anything in traditional American food. Not very sweet, like barbecue sauce. There are cocoa, peanuts (or other nuts) and roasted peppers in it, but they are all mixed together, and none of them have a particularly outstanding taste. Actually, the taste is not familiar. Many people don't like it or even try.

Menudo is one that many people don't like or even try, because it is "weird":

It's made of cow intestines, which explains a lot of problems. Personally, I don't like beef intestines, but I can enjoy homemade delicious food. It is very popular among Mexicans and Mexican-Americans, but Americans who are not very adventurous are not so popular.

Speaking of strange meat, roast goat and mutton (Cabrito) is another kind of meat that has never been popular in America.

This is one of my personal favorites. This is a delicacy in northeastern Mexico (Abela, Nuevo Leon, Tamaulipas), and is usually eaten on special occasions. Many (but not all) Americans don't like to eat meat other than beef, pork, chicken or turkey, so this is a natural rejection. Others complain that lambs, that is, goats, have a "game" they don't like. This may explain why it is difficult to find in restaurants.

The following are not unpopular, but underestimated:

Mexican cheese:

People like familiar things, so people like their Mexican food and yellow cheese, unlike real Mexican cheese. To be fair, I think many people are not familiar with many of them. It is worth noting that Mexico often uses some non-Mexican cheeses, such as Dutch Haoda cheese and Spanish Manchego cheese.

Tacos al Pastor / Trompo:

Delicious pork tortillas were inspired by the cooking techniques brought to Mexico by Lebanese immigrants in the early 20th century. Perhaps the first real "fusion" taco. Although it can be seen almost everywhere in Mexico, it is not popular in the United States. This may be because many local health regulations prohibit the use of "shwarma style" pork in public places, while in Mexico, this practice is usually used in public places. You can cook it in a frying pan, but it's rarely so delicious.