First of all in the author's previous One Shot, the author said: 1 in 10 000 was afflicted by this condition.
Now, either it was a missprint or an error in translation but 1 i. 1 000 is way too common. Either that or the situation is rapidly transforming into a pandemic level of spreading.
You know... as open as GB claims to be, I feel like it's not because it wants to have it both ways, just like their female characters.
Why did the male characters have to accept that they were female and turn into very very feminine women? Why couldn't they continue being just living as female looking men? Because the manga is about cuteness as most GB is. Imagine if a male actually turned into a plain looking girl...
Anyway, to me, GB manga isn't based on realism or real situations, it's all based on attractiveness. Anyone who says that all GB are an allegory for transgender experiences is either not being honest or is wilfully ignorant.
GB manga isn't telling you that humans just flip their sexual preferences on a dime. They are telling you: "Attractiveness makes the world go round". A cute girl is fanservice and can get away with most things. A manly, ordinary-looking girl probably wouldn't.
If we ever get GB manga where the MC turned into a ordinary girl, then the author would really have to put work into selling it to the audience...