This is correlation. Corn (or high fructose corn syrup) is a common ingredient in ultra processed foods, which we already know are the cause of the obesity epidemic. Pre-Colombian societies ate plenty of corn.

It’s also not just about sugar as some other comments have suggested. Humans are built to eats carbs and some tribal people even today get a huge amount of calories from honey without any obesity.

The problem is the way sugar (and fat and other ingredients) are processed in industrial food production. Studies have shown that if you give people food that contains the exact same proportion of fats and sugars, in whole food and junk food form, people will eat more of the junk food. This is the problem. Whole foods are generally all fine.