We humans have been around for hundreds of thousands of years, and for most of that time, food has been hard to get. We’ve had a relatively stable food supply (thanks to agriculture) for only about 10,000 years.
Now lots of people have weird relationships with food. For example, did you know that if you are offered varying amounts of food on a plate, you’ll end up eating more if there’s more food on the plate? This can happen regardless of how hungry you are.
Welcome to the famous portion size effect.