Well, in some fanfictions, it could be that they're under the influence of some dark magic or a spell that makes them turn against Hermione. Or perhaps they're misinformed about her actions at Hogwarts and think she's a bad influence. Also, some writers might use it as a plot device to create a rift and then build a story around Hermione trying to fix things with her parents.
Well, it could be possible in some really out - there fanfictions. Maybe some writers want to create a lot of drama. They might think that if Hermione's parents suddenly turn against her, it can add some really intense emotional turmoil to the story. But in the original books, Hermione's parents are really supportive.
There could be some underlying mental health issues within the family. Perhaps her parents have some undiagnosed conditions that make them more prone to lashing out. In the fanfiction world, this could be explored further, like how Hermione tries to understand and deal with this aspect of her family situation while also dealing with the abuse.
One possible reason could be her involvement in the wizarding world. If her parents are muggles and they find out about the extreme dangers she faces in the magical realm, they might disown her out of fear for her safety. Another reason could be if she starts to show more loyalty to the wizarding community than to her muggle family, making them feel like she no longer belongs with them.
One possible reason could be social class differences. Hermione's parents are Muggles and might view Ron's large, wizarding family with some prejudice. They may see the Weasleys as a bit chaotic and irresponsible because of their financial situation.
It might be due to cultural differences. Hermione comes from the wizarding world, and Annabeth from the demigod world. In fanfiction, these differences could be exaggerated, and Hermione might find Annabeth's 'alien' culture off - putting or difficult to understand, leading to dislike.
Perhaps in this fanfiction, her parents have some secrets that Hermione discovers. These secrets could be related to the wizarding world and their connection to it. Their attempts to hide these things from her make her feel betrayed and thus lead to her hatred. For instance, if they knew about some dark magic in their family history but kept it from her.
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.
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.
Some people might just want to explore alternative scenarios for the sake of creativity. They may think it's interesting to see how the story would unfold if there was animosity between them.
In this fanfiction, it could be that Naruto's parents were under some sort of mind - control. Some evil entity could have taken over their minds and made them feel hatred towards Naruto. Also, it might be related to a family secret or feud. There could be something in the family's past that made them believe Naruto was a stain on their family name, even though Naruto himself was innocent. It could also be a case of false information being spread around the village which made his parents believe lies about him.