I think you're misunderstanding. There is no "natural set point." The set point moves up and down based on hormones, genes, diet, environment, medication, etc. And the very act of gaining weight causes your body's set point to move up, because of how weight gain affects your hormones. Unfortunately the set point is pretty sticky, and once it moves up, it does not like to move back down, in part because for most of animal history, weight loss is a sign of starvation.

Today, there are a bunch of factors that have combined to move people's set points higher than they should be: calorie-dense diets, sedentary lifestyles, plastics, drugs like antidepressants and lithium compounds in the water supply, and who knows what else. No one is arguing that the "natural" set point is 300 pounds or whatever. The point is that there is no natural set point because it's a function of many different variables.