The top and bottom of that range is an entire meal difference. Or put another way, if two people on opposite ends of that range eat 2320kcal daily, we expect the person with the lower metabolism to gain 50lb a year. Awesome.

This is where you come in and say, "Oh well, the person with the lower metabolism should eat less." So now the person with the lower metabolism has to eat a meal's worth of food less than the other person just to maintain their weight to say nothing of losing it. And I'd wager the person providing their body with 1600kcal is probably feeling sluggish and depressed all day. Which is why I include willpower.