It started with pet food. Attempts at making plant based foods for dogs and cats initially failed, becuase the animals didn't want to eat these unnatural diets. But a solution was found: the so called "palatants". When they were added to the food, animals ate it.
Naturally, somebody thought of using these in human food as well. It didn't work as expected - it turned out they don't work by making the food tastier, they work by disabling the satiety response. Once the palatants get into your bloodstream, you won't feel satisfied no matter how much you eat until your body can get rid of these these chemicals. You may feel that your stomach is completely filled and stop eating, but you won't ever feel that you ate enough.
Since adults would get suspicious if they got more hungry, it started with child menus. The idea was the same as with pet food - if children eat a lot of the food, their parents will buy it again.
Now we have at least two generations of people who believe it's perfectly normal not to feel satisfied until their stomach can't hold any more food and that staying not obese requires arduous discipline. Our perception of normal weight has changed as well, for pets and human alike. Cats, when fed unaldutered meat eat to stay very skinny, with body shape that many modern guidelines show as "very thin" or "underweight". But many people today think of them as naturally fatty animals.
Many of these chemicals are approved food aditives and are listed usually as emuglators, flour conditioners or something similarly inconspicious.