> Why not? It's a skill necessary to adapt to circumstances our bodies didn't evolve in (that is constant and unlimited access to food)

Perhaps not normal bodies, but certainly some bodies. I don't count calories. Sometimes I eat ridiculously large meals. Sometimes I snack on calorie-dense foods all day. But my weight has been basically constant since I stopped getting taller. Although I haven't measured it, it must be that I'm compensating by eating less (or at least less energy-dense) on other days. I do this without trying, or even thinking about it: I simply eat as much as I want to, whenever. When other people do the same, they gain weight. Obviously, they're eating more calories than they're burning, and I'm not, but why?