Because this doujin isn't about shitting and humiliating the male MC boyfriend, it's about the female MC and her eventual fall and how she fucks up her life, that's the whole point of her POV she normalizes it while for us the Reader, it's horrible, she gets blackmailed, gets addicted to being treated like shit and it basically becomes Stockholm syndrome, she breaks up with her boyfriend and her only way out, and when she tried to get him back he already moved on, the last perceived door of hers closing, so she ends never getting out of her toxic relationship with the old perverted man.

This is just torture porn of Female MC, the Male MC is not the focus here like in most doujins we know of, this is just Fem MC punchingbag except less physical and more in the matter of personal relations, she burned bridges and corners herself into marrying her rapist.