In fanfic, the author might want to show a different side of Harry. He has always been brave in the original story, but by having him study seriously, the author can develop his character further. He could be on a journey of self - discovery through learning. He might also be trying to live up to the expectations of those who believe in him, like his friends or professors, and so he devotes himself to serious study.
Perhaps he has a newfound motivation. Maybe he met a new mentor who inspired him to take his studies more seriously. Or he could have witnessed something that made him realize the importance of knowledge, like seeing someone get defeated because of their lack of understanding of magic.
One reason could be that he's desperate for any form of guidance. After all the chaos he's been through, divination might seem like a way to get some answers about the future. It's like grasping at straws, but it could be important to him.
One reason could be to save him. Maybe Harry is injured during a battle or some sort of magical accident, and Snape, despite their differences, steps in to carry him to safety. For example, if Harry is hit by a dark curse and Snape, with his knowledge of dark magic, knows he needs to get Harry to the infirmary quickly.
Another reason could be that Harry has other priorities in the fanfic. He may be more focused on solving a mystery, helping a friend, or achieving a personal goal that doesn't involve fighting. So, fighting is not on his agenda.
One reason could be that the fanfic distorts the characters he knows well from Gryffindor. For instance, if it changes the personalities of his friends in Gryffindor in a way that doesn't seem right to him.
Maybe in the fanfic, there could be a misunderstanding between them. For example, Ron might have accidentally broken Harry's trust in some way, like revealing a secret of Harry's that he wasn't supposed to.
One reason could be revenge. Bellatrix might want to get back at Harry for causing problems for Voldemort and the Death Eaters. Kissing him could be a form of humiliation. Another reason could be a power play. By kissing Harry, she shows that she can get close to him and has some sort of control over the situation.
Maybe Dumbledore discovers some dark secret about Harry's past that he can't handle. It could also be that Dumbledore is trying to protect Harry in a really strange way, by pushing him away from the dangerous wizarding world around Hogwarts.
Maybe in that fanfic, there are misunderstandings between Harry and the Weasleys. For example, they might have had an argument over something like magic use or family values that led Harry to dislike them.
One possible reason is that the fanfic writer wants to create conflict. By making Hermione not believe Harry, it adds tension to the story.
The fanfic might be set in an alternate universe where Ron has a different personality. If this new personality clashes with Harry's values or his own personality, then Harry may not like Ron. For example, if Ron is made to be more self - centered in this fanfic, Harry might find it hard to get along with him.