Why are so many of them obese? It’s like none of these Mexicans ever bothered to lift or do cardio.
Myrtle my Turtle. Let me introduce you to something very interesting.
This here is Yalitza Aparicio. She's from southern Mexico, I want you to take a good look and understand that this is what a "Native Mexican" from that area looks like when there's little to no Euro in it.

Note things like the rib cage. No amount of starving herself will shrink it or make her taller. It is what it is. (Though that doesn't stop people like
the Demon of Miami from trying to pathologize it and get women with this body type to mutilate their ribs.)



They are a "sturdy" people, that's the explanation for why the fat sits where it is.
As for
why the fat exists, there are a lot of elements there. Part of it is a similar phenomenon to what happened to the Italian Americans who came over and then suddenly had access to ingredients that were once luxuries and used them to create new things that weren't "authentically Italian" but reflected the flavor preferences of the Italian people.
I say all this because while it would be reductive and dismissive to say "Because they're just a bunch of big stupid fatties", the culture they came from
did lead to shit like:
Bisabuela: "I can afford beef now! I'm going to put ground beef in with these spices and make chili."
Abuela: "Tortillas and pre-shredded are being sold in stores now. This saves me so much time and I can make even more food for my family."
Mom: "The TV man says Fruity Pebbles are part of a complete breakfast. It must be true. I'll have cereal for breakfast and make tacos for dinner."
Child: "I grew up with hyperpalatable foods and my culture is 'cool' now. I'm going to snack on takis, drink Jarritos, and then get street tacos fried in canola oil."
And also, you know, corn syrup and seed oils, same as everyone else.