I can imagine all those self-hating mangaka praying at the shrines for a blonde European or American woman they can burden with their whiny demands to be pampered and treated like a child or a slave
And this whithout a care for the personal problems of those blonde girls or for the fact that (shock! Horror!) many of them might actually be more fragile, traumatized, insecure and submissive than they are.
Manga are pictographic. They use images as short-hand for ideas. A blonde should not be taken as literally blonde, just as a character suddenly drawn in blob-like manner should not be taken to have begun dissolving, and an enormous sweat drop should not be taken as representing monstrous perspiration.
It's super neat how those have not been forgotten since they were bought in chapter 2. Nor do they end up becoming a big plot point, just important accessories for those two adorkable lesbians.