Because we only feed in the United States less than 1 per cent of the meals, most of them are eaten elsewhere. Most meals are eaten at home. So to make McDonald's the target is not going to solve the problem.
Civilization never stands still; if in one country it is falling back, in another it is changing, evolving, becoming more complicated, bringing fresh experience to body and mind, breeding new desires, and exploiting Nature's cupboard for their satisfaction.