Something I think that contributes a lot to how much weight you hold naturally is how insulin sensitive you are. The more insulin sensitive you are the less weight you'll put on and there's a huge range between optimal insulin sensitivity, average, and diabetic.

I also suspect (although I'm not an expert) the reason some people find it easier to lose weight while doing OMAD or keto isn't just because they're eating less, but because they're far more insulin sensitive and two of the best ways to increase insulin sensitivity is to fast or to eat less carbs.

Another reason I believe this to be the case is because as I've aged I've noticed my friends are holding more weight despite little change their diets or physical activity. I'm sure some of this is related to a slowdown in their resting metabolic rate, but I also suspect it's got something to do with the fact that as people age they become less insulin sensitive on average -- especially if they don't eat well or eat too often. This is probably why as a kid you can eat a tub of icecream without putting on any weight, but as adult you would. It's not just that kids have higher metabolisms, but that they're more insulin sensitive and less likely to be diabetic or pre-diabetic.

A question to ask here is why are people with low BMI's are less hungry? Could that be because they're metabolic healthier and their bodies are therefore better able to enter ketosis during periods without food? From personal experience with fasting and low carb diets I've experienced how significant it is when the body adjusts to burning fat as a primary fuel source. Although, you still feel hungry you don't feel like you need food. Similarly, you know when someone isn't metabolically adapted when they go too long without food because they become irritable and physically feel week.