Because it's simply not reality and people can differentiate between the two. Just because you like any tipe of fetish in a manga/novel, doesn't mean you want that to happen in real life. For example some people may enjoy incest stories, but that doesn't mean they want to get it on with their siblings. It's called fantasy for a reason. It's fine if you don't like it but everyone is different. That's way I'll never understand people say "it's 2024 stop with the rape plot". It's just a fantasy, not reality and if some people don't like it they can just stop reading it without bothering and making a huge mess. Personally I don't mind it here simply because both of the characters are trash so better two pieces of shit together than with other people.
If you guys wouldn’t mind answering a serious question. This is no shade but genuine curiosity how could you like the side couple. I don’t think rape is ever ok, nor is it sexy or a turn on. Why do you think he deserves to be brutalized like this? Not saying his actions were ok, but he doesn’t deserve to be consistently brutalized either. So why are you enjoying this so much? Sorry if that sounds rude but I really don’t get the appeal unless you enjoy rape or something.