One possible reason could be to gain extraordinary powers. In some fanfictions, giving up humanity might be a sacrifice for a greater magical ability, like being able to control all elements or access a new level of magic that is otherwise inaccessible to humans.
The overall theme of the story changes. Instead of a story about a human wizard's journey, it becomes a story about identity and transformation. It may explore themes like what it means to be human, and whether giving up humanity is truly a sacrifice or a gain. This can attract different types of readers who are interested in these deeper, more philosophical themes in fanfiction.
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.
It could be a case of misinformation. Someone in the story might have spread false rumors about Harry being the father for their own motives. Perhaps they wanted to cause chaos or gain something from the situation. So, the whole idea of Harry being the father is just a false story that gets spread around the wizarding community.
One reason could be to show a more complex side of Harry. By making him the heir of Slytherin, it blurs the lines between the houses and shows that he has qualities from different aspects of the wizarding world.
Another reason might be related to his magic. There could be some sort of magic interference or a spell gone wrong that affects his ability to speak freely. Maybe a curse was placed on him that makes him mute in specific circumstances, or there's some internal magic struggle within him that causes this selective muteness. This would add an interesting layer to the story and could be explored in many different ways in the fanfiction.
One reason could be to give him a stronger connection to Hogwarts. As the heir, he might have special privileges or knowledge about the school. Another reason is to add a new dimension to his character. It makes him more than just a student who defeated Voldemort.
One reason could be the aftermath of his battles. For example, the physical and mental scars from fighting Voldemort. He might be in pain from the Cruciatus Curse that some dark wizards in the fanfiction might use on him. Another reason could be the loss of his loved ones. Losing Sirius, Dumbledore, and others could cause him deep emotional pain that manifests in the fanfiction as a constant ache.
One reason could be for creative exploration. Writers may want to see how the story changes when the main character has an androgynous appearance.
He might have more free time for other hobbies like reading regular books or watching movies.