Because in japan raped is no big deal and they rarely do anything about it even if you file a report. They have different words for rape depending on the type.
That is not really true rape is gone after just like any other crime in any other country. Jpn. culture is often mis understood. It is not all in the manga.
WTF... her husband raped her son and she like it is nothing and even said she must be with her husband... scary!!!
And all of them act like that rape was nothing bad!!! Ughhhhh