alt Hacker NewsThat 2400 number?
It is an average. A guideline. And most countries give an average or range. And the US isn't the highest here: The official recommended averages I found after moving to Norway were higher than in the US and much more reasonable to keep to. (I'm female, my averages are lower).
That doesn't mean that the food pyramid is a good thing or that we've been giving good health advice. It also doesn't mean that our health advice is all that good now. We know more than we did before, but nutrition science seems tricky to do and even trickier to communicate well with the general public in ways that most people can follow. And that's before the disinformation from business interests and dealing with outright scams and lies.
Here's the thing: It may be that 2400 calories would take the average 40 year old male and only have him continue the socially acceptable weight gain of a few lbs a year. Or maybe the average (already overweight) male would maintain his weight at 2400 calories.
But in any sane world, that's like the 90th percentile of calories required when consumed with a carb-heavy american diet and I'd argue almost no sedentary person requires that much. Just plugging in the basal metabolic rate numbers gets something well below that.