Because if she is the main heroine, she'll overpower all other heroines
). And I guess Japanese's taste is weird, see how many novel have a pink hair tsundere girl as main heroine already
), oh god they must be either pink or blond. Almost all of Japanese are god damn masochist who like to be whipped. All the common long black beautiful hair cool personality heroines are just pepbles to step on for service.
Oh and when I say 2 dimensions, I mean the kind of literature that make you feel something broken in you as a human and the kind that just make you feel sad but more human.