Perhaps in the fanfiction, Edward tries to control Bella's life too much. He might be overly possessive, not allowing her to have her own friends or pursue her own interests. This overbearing behavior can easily make Bella resent and eventually hate him.
One scenario could be that Edward accidentally endangers Bella's family in the fanfiction. Since Bella is very protective of her family, this could be a major turning point for her feelings towards him. For instance, if his vampire nature attracts some dangerous vampires to Forks and they target her family.
In some fanfictions, Edward may break Bella's trust in a significant way. Like lying about his true identity or his relationship with other vampires. When the truth comes out, Bella, who values honesty, would be deeply hurt and could turn that pain into hatred for Edward.
One possible scenario is that Jacob reveals a secret that Bella doesn't like. This could make her feel betrayed and start to hate him.
One possible scenario is when the imprint causes Jacob to be very protective of the person he imprints on. Bella might see this as Jacob neglecting their previous friendship or bond. Another scenario could be that the person Jacob imprints on has a negative attitude towards Bella, and Jacob seems to side with the imprinted one, making Bella hate the whole situation.
One possible reason could be that some fans want to explore a different dynamic. In the original story, Edward and Bella are in love, but in this fanfiction, perhaps the writer wants to show a more complex relationship where Edward hates Bella. Maybe it's to add more drama or to explore an alternative storyline that goes against the typical romance.
One reason could be that some fans want to explore different character dynamics. The original Bella - Edward relationship is so well - known and often idealized, so making Bella hate Edward creates a whole new set of tensions and story possibilities.
One possible scenario could be that Bella meets a new vampire who has a very different charm from Edward. Maybe this new vampire is more carefree and shows Bella a different side of the vampire world that she becomes attracted to, leading her to cheat in the fanfiction.
Maybe in the fanfiction, Bella wears Edward's clothes as a statement. It could be a way for her to show that she belongs to him in a sense, or that she's part of his world. She might put on his shirt before going to meet his family, for example, as a sign of respect and acceptance of their relationship and his vampire lifestyle.
One common scenario is when Edward loses control. Maybe he gets too close to Bella when he's thirsty for blood, and she can see the struggle in his eyes. This nearness and the thought of him potentially harming her can be terrifying for her.
Perhaps in the fanfiction, Scott falls in love with someone that Stiles also has feelings for. This love triangle situation could turn Stiles' feelings into hatred as he sees Scott as a rival for the person he cares about. Also, if Scott accidentally reveals one of Stiles' secrets that he promised to keep, Stiles would likely be very angry and could start to hate Scott.
One possible scenario is that Minato was resurrected in a wrong way in the fanfiction. His behavior after resurrection was not what Naruto expected. Maybe he was more cold - hearted or seemed to have different priorities that didn't include Naruto, so Naruto started to hate him.
It could be that Percy gets involved in a conflict where he sides against Artemis' hunters. His actions in this conflict might make Artemis view him as an enemy. For example, if he accidentally harms one of her hunters while trying to protect someone else, she may grow to hate him.