This is a common archetypal theme of "beauty & the beast" found in fairy tales, myths, & other storytelling mediums (like some Guillermo Del Toro's movies). It conveys the healing & redemptive power of love/Eros, which is feminine in principle. That's why the lover-healer is called as the Beauty & often personified as a female character. It shows how love — as a radiant & transformative grace — can tame, heal, & redeem even a wild, dangerous, or grotesque beast/monster.
Caution: This theme should be understood symbolically, not literally. It shouldn't be taken as a model for real life relationship too (because it could bring a lot of troubles for the woman, or practically bordering to the pathological; find yourself a decent man, not a wounded beast, ladies!).
Note that the stories & events in fairy tales/myths are often completely whimsical or even nonsensical (some people had literal interpretation for the story "Beauty & the Beast" & think of the woman as having Stockholm syndrome, which is mistaken). This is because these stories don't operate according to linear & rational rules. They operate within a symbolic order instead & need to be understood more intuitively.
Guillermo del Toro understands that women long for the beauty buried inside the monstrous