The whole reason is control. It’s much easier to control the sheeple if they are in centralized FEMA camps which comprise complete cities. They are then totally dependent upon the government for heat, light, food, ..... everything!
Watch for cultures and groups within the country who are independent and self reliant to come under scrutiny and attack. this is especially true if they answer to a higher authority than human government authority. Mormons, Amish, and some other groups come to mind.