One reason could be that Jacob realizes they have different life goals. Bella is often so focused on Edward and the vampire world, and Jacob may feel that his werewolf life and values are too different from hers to have a romantic connection. For example, he might want a more traditional werewolf life with his pack, while Bella is constantly drawn to the dangerous and alluring vampire lifestyle.
It could be that Jacob meets someone else in the fanfiction. This new person might share his interests, values, and understand his werewolf nature better. With this new love interest in his life, his feelings for Bella fade away as he realizes that what he thought was love for Bella was more of an infatuation or a result of the pack - vampire rivalry.
One possible reason could be that Renesmee simply has different interests. Maybe she is more drawn to a different lifestyle or set of values that Jacob doesn't align with. For example, she might be interested in exploring the world in a more solitary way while Jacob is more about the pack and community.
Perhaps Jacob could start to spread negative rumors about Bella among their mutual friends. This would create a rift not only between them but also within the larger group that they are a part of. He may feel betrayed by Bella for some reason and wants others to see his side.
The plot could develop with Jacob focusing on his own growth and self - discovery. He might leave Forks to explore other werewolf packs or just to be on his own for a while. This would create a distance between him and Bella, and the story could then show how Bella reacts to his new - found independence.
One possible reason could be a change in character development that diverges from the original show's trajectory. Maybe in the fanfiction, the writer wants to explore new relationship dynamics where Castle has different feelings. Another reason might be to create conflict for the plot. By having Castle not love Beckett, it can lead to a series of events that test their partnership in a different way.
A possible storyline could be that Bella discovers a long - lost family and gets involved with them, putting all her energy into getting to know her family members and heritage. Since she's so occupied with this new aspect of her life, Edward becomes an afterthought. Another storyline might be that Bella becomes a strong advocate for a cause, like protecting the environment or helping the less fortunate. Her focus on this cause is so intense that any feelings she might have had for Edward fade away. And perhaps in some fanfiction, Bella gets involved in a time - travel plot where she goes back in time to change certain events, and in this new timeline, she doesn't fall in love with Edward.
One reason could be Jacob's more down - to - earth nature. He represents a more normal, warm - hearted life compared to Edward's rather cold and sometimes brooding vampire existence. Bella might be drawn to the simplicity and closeness to nature that Jacob offers.
Perhaps in the fanfiction, Edward broke a significant promise to Bella. Promises are important in relationships, and if he failed to keep one, it could lead to her not forgiving him. For example, if he promised to always be there for her but then abandoned her in a time of need. Also, his over - protective nature in a wrong way could make Bella feel suffocated and less likely to forgive him.
Maybe in the fanfiction, Vegeta has some personal growth that makes him focus more on himself rather than family. He might have new goals and ambitions that he thinks are more important than his relationship with Trunks.
There could also be other characters from the Twilight series involved. For example, the members of Jacob's wolf pack might play a role. They could be trying to mediate between Jacob and Bella, or they might side with Jacob, adding more tension to the story.
It could also be that Jacob has his own ideals and values when it comes to love. He has this image of being with Bella in his mind, and the imprint doesn't fit into that. He might feel that his feelings for Bella are pure and true, while the imprint seems like a more primal or instinctual thing that he doesn't want to succumb to. So, in order to stay true to his own sense of self and his feelings for Bella, he rejects the imprint.