Perhaps it's because Harry Potter is used to the real Hermione and the real events in their lives. Fanfiction often adds elements that are not part of their actual experiences. He may feel that these fictional additions take away from the purity of their relationship and the events they've been through. He values the original narrative and the way things actually happened in the wizarding world more than the creative but sometimes inaccurate fan - created stories.
Another possible reason is that Harry is protective of their story. Fanfiction can be quite wild with different interpretations, and he might not like how some fanfictions try to rewrite their relationship. He has a deep - seated understanding of his bond with Hermione, and fanfiction that messes with that can be hard for him to tolerate. He might think that the real story is already great and doesn't need these made - up alterations.
One reason could be that the fanfiction changes her personality traits. In the original, she's kind - hearted but in fanfic, she might be made mean. Harry, who knows the real Molly, won't like this new version.
One reason could be that the fanfic writer portrays Ron as overly jealous of Harry. In the original books, Ron has moments of jealousy but not to an extreme. If in the fanfic it's overdone, Harry might not be able to stand him. For example, if Ron is constantly trying to undermine Harry's achievements out of jealousy.
Fanfiction can sometimes deviate a lot from the original story. It might be that the official creators or those in charge of the Harry Potter brand don't want the characters to be misrepresented in fan - made stories, so they restrict access to it for Harry or anyone in the context of that world. Another aspect is that some fanfiction may have a negative or unethical undertone, and to protect the integrity of the original story, access is prohibited.
One possible reason could be that he was injured during a battle with dark wizards. Maybe he was hit by a powerful curse that affected his legs. Another reason might be related to some kind of potion gone wrong. For example, if he accidentally drank a potion that had negative side effects on his motor functions.
One reason could be his pure heart. Harry has shown great courage and self - sacrifice throughout his story, which might be seen as 'worthiness' in the context of Mjolnir.
One reason could be a reaction to the Ministry of Magic's mismanagement. In the original story, the Ministry often made mistakes and had corrupt elements. In fanfiction, this could lead to Harry becoming an anarchist as a way to oppose such a flawed system.
One reason could be to add more depth to his character. Schizophrenia can bring out complex emotions and behaviors, making Harry more relatable in some ways.
One reason could be the author's desire to rewrite the relationships in a more edgy way. They might think that making Hermione mean to Harry will attract more readers who like drama.
One reason could be his status as the Boy Who Lived. In the original story, Harry has this special aura about him, and in fanfiction, Hermione might be drawn to that in an obsessive way. Also, his bravery and leadership qualities could be factors that make Hermione overly interested in him.
One possible reason could be that the magic used against him is of a very dark and ancient nature that defies the normal healing spells. For example, if it's a curse created by a long - forgotten dark wizard with unique and unbreakable properties.