I think some supermodels may appear so grim, because of too much makeup that makes them look artificial. It may also be because they don't represent a day to day woman, but they tend to focus more on an illusion.
Some possible explanations would be: The unrealistic expectations set upon them. They wish they could eat a bacon cheese burger. They can still taste the vomit from the last meal they purged. ...Or you are a chubby chaser.