Are you sick to your stomach of beautiful princesses? Yeah, we are, too. Fairy tale appearances tend to be extreme when they're mentioned at all; someone's either the fairest in the land, or not worth describing at all. Appearances also have an interesting correlation with inner states in Grimms' Fairy Tales. We see characters who are beautiful and virtuous or beautiful yet wicked, but rarely do characters get described outside those poles. To be fair, who wants to read about The Average-Looking Princess Who Was Mostly Nice But Occasionally Snide?
There's no worse fate in fairy tales than being ugly.
The idea of inner beauty is nice and all, but fairy tales are more about surfaces than interiors.