it's one of the dumbest logics you'll see out there, it's not surprising people don't get it.
Funnily enough it works backwards irl, a lot of "pure" girls in japan are way more likely to be batshit insane just hiding behind a pure and squeaky clean persona, and they get away with it by being cute and acting pure.
On the other end you got gyarus, japan's anthetesis of purity, they are incredibly descriminated against but that also makes them more openminded and chill, but since people really care about how you appear to be and not really who you actually are they prefer to side with the "pure" girls.
(it's just a general feeling of how things are perceived, not all people are like this)
fortunatelly times are changing and young people in japan are way more connected with western culture probably because of the internet.
Rip their birthrates tho, they dying, if only they allowed more foreigners looking for some japanese ladies, since all they guys there are too occupied simping for anime waifus