I am sure some people have it bad. (But having a full stomach and satiation has nothing to do with each other for me, I suppose it’s true for many others…)
But… People are different and their diets are different too. My SO who is a very convenient example when I talk about high-carbers… Well, he gets satiated by less food than I do and it lasts way longer. He just needs and eats more per day (except when I don’t behave as I easily leave him behind by far). I would STARVE on his food
WAY too much carbs and not nearly enough protein for me there. The fat intake is lovely, more than mine, probably but it depends on the day. There is a big difference between a breakfast made by him and one made by me, for example - but both are the same satiating for me. 90% carbs or 10? Doesn’t matter, apparently.
But it does A LOT to me. I just don’t know what is it for the average person… It seems most people gets satiated by carbs way better than me, people ate carby during history, we saw people eating a sandwich or two and being fine (how they do it I can’t imagine :D)… But (just on this forum) I heard about people being hungry on high-carb too… But why don’t they eat differently then? I got high satiation on high-carb every time, I needed it so I just ate until it happened, whatever I desired or had. I overate epically several times because carbs have that effect on me. They make me hungry and they are triggering too sometimes so I easily ate a ton after reaching satiation. I can eat carbs and fats in scary amounts as I don’t reach a stop sign unless 1. my stomach gets full but that’s near impossible without using soups or something 2. I start to feel unwell and heavy due to massive overeating 3. I just get bored of eating. Sometimes I wonder what could have happened if I didn’t eat so much protein all my life… I NEED that for satiation. It was bad enough on high-carb without that problem… That can be the problem for your family, maybe? Not getting enough protein? But it easily can be just the carbs. It’s actually weird. The body gets energy galore and it still gives us hunger signs. No matter if we got all the nutrition we possibly need - but this may be less common, I don’t know but I have it.
And we know people who are just fine on high-carb, no overeating ever… I don’t believe all are hungry a lot, it wouldn’t make sense knowing people. (And there is my SO who gets satiated somewhat worse on low-carb. But it was so bad he only tried once, I just know that the super rare low-carb meal isn’t more effective than his carby ones and too much fat - percentage, much fat without the carbs - causes problems like nausea and delayed satiation so he overeats and regrets it.)
Oh and plant net carbs make me hungry on keto too. Some of us are more sensitive to the carbs when it comes to satiation and hunger. Maybe my SO is fine because he doesn’t eat insanely high carbs - but it’s always high. But carbs satiate him - at least in the presence of some fat and protein. He needs way less of those. So maybe we just have our lower limits for satiation regarding the macros - if we totally oversimplify it. But no, there are the people who just need their calories, the minimum fat and protein and that’s it. So HCLF and LCHF both work for them. It makes perfect sense, add the body the essentials, energy can come from carbs and fat alike… But due to the hormonal effect of carbs (and who knows what else, not me), it’s often not the case. But why it is for some people? Whenever I think about how most people eat, how people ate during history - all those carbs and multiple small meals - , I wonder what would have happened to me if I was forced to eat that way too. As now… It doesn’t work. I am starving that way. I never could eat a sandwich and get satiated for a while. Could I? Maybe in the morning when I had no need for food anyway (the sandwich definitely made me hungry way earlier though, I hated breakfast and stopped when I got big enough for it).