packaged dead food-like substances and industrial junk food are everywhere, convenient, low-cost, high-calorie, engineered by scientists to be irresistable, habit-forming.
Doctors aren't educated on nutrition, why do you think uneducated, poor people, esp blacks and Hispanics, would know about healthy nutrition?
TV shows have plenty of overweight and obese people as "acceptable" characters.
The govt-approved S.A.D. Standard American Diet is pathogenic, too many carbs, too much meat and dairy (as dictated by subsidized BigFood/BigAg).
Even sit-down "casual dining" restaurants put way too many calories on the table, to give people their "money's worth".
One has to be quite "radical" to resist, to escape from the pathogenic BigFood toxic, pathogenic universe. There's even pejorative terms for people who are conscientious eaters: "foodie" and orthorexic.
Poor people in ty environments are under never-ending financial, social stress, where food really is stress-relieving, comfort food.
When 150M+ people in USA are overweight, obese, it becomes the accepted, implicit norm, the way "average" people should look.