In Game of Thrones director had a chance to make the dwarf (protagonist ) really ugly, like in the books, but they chose a good looking actor.
Same for Harry Potter, Hermione was supposed to be meh.
Now most actors in popular media are good looking to an uncanny level. Antagonist are beautiful too (in GoT as well).
It's not surprising if this negatively affects the psyche of the everyday person.
- People who crave validation seek good looks. They want to be accepted.
- People who crave status seek good looks. They want to be awarded.
- People who crave admiration seek good looks. They want to be desired.
There are so, so many more possible reasons and motivations, and it highly depends on the individual. Someone could have all of the above or none of the above and still obsess over looks. Someone could obsess for different reasons in different contexts or with different moods.
It's not based on some infantile monkey-see-monkey-do obsession with media.