All animals have evolved instincts and reactions to stimuli they ordinarily encounter. For example, birds protect things that look like eggs, because ordinarily if something looks like an egg, it is an egg. And they'll protect larger eggs rather than smaller eggs, because more resources go into creating a larger egg.
But in a scientist's lab, something that looks like an egg might not actually be an egg. And in such circumstances, birds will protect large non-eggs more than small eggs. They respond to the stimulus even when it no longer indicates what it ordinarily indicates, and the stronger the stimulus, the stronger the response.
We are just as susceptible to this as other animals. In our ancestral environment, sugar and fat were hard to come by, so when it did come by, you wanted to eat as much as you could while it lasted. So sugar and fat taste good, and they keep tasting good even when they are no longer in short supply.
Superstimuli are a large cause of today's obesity epidemic. Ice cream and cheeseburgers have more concentrated sugar and fat than anything a hunter-gatherer could get, so they trigger a stronger response.
Superstimuli apply to more than just food. Models are made-up and airbrushed to look more perfect than any real person ever could. Our modern society is inundated with superstimuli. Movies, television, computer games, the internet, porn. These all provide stronger stimuli than you could ever get otherwise. And when the stimulus becomes disconnected from the benefit it provides, the response does as well.