I have seen this so many times anecotally too. It’s not even “metabolism” so much as it is how hungry people naturally get. It varies so much from person to person. I could easily eat 4000kcal a day and feel hungry if I have anything less than 2200 or so whereas I know “hard gainers” who struggle to eat more than 1000kcal in a single sitting.

However I don’t think it’s purely genetic/intrinsic. At least personally I have seen that after a period of dieting my natural hunger reduced to about as much as I had been eating.

Anyway, I agree that these restrictive diets work in general by making it easier/necessary to count calories and eliminate some junk food. Really, eliminating dense addictive foods and counting calories is probably all the vast majority of people need to do to lose weight