Perhaps in this fanfiction, Ron's loyalty is in question. Harry and Hermione value loyalty highly, and if for some reason Ron is portrayed as being unfaithful or unreliable in the story, it could cause them to dislike him. For example, if he were to side with someone against Harry and Hermione's best interests, that would be a big factor.
It could also be related to their individual goals. If Ron's goals are not in line with Harry and Hermione's, especially in the context of fighting against the Dark forces or achieving something important at Hogwarts. His lack of focus or different priorities might make Harry and Hermione look at him unfavorably in the fanfiction.
Another reason could be that Ron's academic performance is not as good as Hermione's. Hermione is very studious and intelligent, and her dad might expect her to be with someone who is also academically inclined. Ron, on the other hand, is not as enthusiastic about studying.
It could be due to a misunderstanding. Suppose Ron overhears a conversation between Harry and Hermione that he misinterprets completely. He might think they are plotting against him or don't really consider him a true friend. So in a fit of anger and hurt, he decides to betray them.
It could be due to a misunderstanding that got out of hand. Ron and Hermione might have been involved in something that Harry misinterpreted as a sign of their disloyalty. For instance, they were secretly working on a project that Harry thought was against him, but in reality, it was for his own protection. However, because of the lack of communication, Harry's anger and unwillingness to forgive grew.
One reason could be envy. Hermione is often very good at academics and magic, and Harry and Ron might be envious of her success. For instance, if Hermione always gets top grades in potions class while Harry and Ron struggle, they could lash out at her out of frustration.
One reason could be jealousy. Maybe Ron feels that Harry is getting too close to Hermione and he's afraid of losing her attention. In fanfiction, authors often play with the characters' emotions. Harry, on the other hand, might see Ron as being too possessive of Hermione.
One reason could be the Malfoys' pure - blood supremacist views. Harry, who has a more inclusive and open - minded attitude, would naturally oppose their discriminatory ideas. The Malfoys often look down on those with non - pure - blood heritage, and Harry, having friends from different backgrounds, would not like such snobbish behavior.
It's possible that Harry hates it because he has a certain image of Ron and Hermione in his mind. Fanfiction can sometimes create versions of them that are completely different from what he knows. For example, some fanfiction might focus on a love triangle that he doesn't think exists in their real relationship. This divergence from his perception could lead to his dislike.
Power could be a reason. If there's a chance for Ron and Hermione to gain a great deal of power by turning against Harry, some fanfictions might explore this. For instance, a new dark power might offer them something they've always desired, like the ability to reform the wizarding world in their own image. They might think Harry would oppose this, so they betray him to get what they want.
One possible reason could be a misinterpretation of their relationships. Maybe the author wants to explore a different dynamic where Harry and Hermione bond over Ron's perceived flaws, like his occasional laziness or his insecurities that might come across as annoying to them in this fictional scenario.
Well, perhaps in the fanfiction they leave because of a prophecy. A prophecy might state that their presence near Hermione would bring great danger to her or to the wizarding world as a whole. So, they sacrifice their friendship and leave. Also, it could be due to some dark magic influence. They are forced by a powerful dark magic spell to stay away from Hermione, not having control over their actions.