Isn't that because calories aren't really directly relevant to how people shop for food or consume it? I can't just replace a hamburger with 10x that amount of

Isn't that because calories aren't really directly relevant to how people shop for food or consume it? I can't just replace a hamburger with 10x that amount of grain, or even 1/10th of that amount of grains and get the same nutritional values. For the most part, feed grain for cattle isn't even grains that most humans would eat without plenty of calories of processing by other humans put into it. In general, I feel like you're conflating "modern" with "luxury" in a way that doesn't feel reasonable. Just because we haven't being doing something for long, or that it requires effort/inefficiencies doesn't mean it's innately "luxurious". Certainly not everything modern is good, but almost everything about food even in non-western countries is calorie inefficient and relatively modern as we invented new ways to cook and farm, and spices and cooking methods became more diverse.