One reason could be that the fanfic might distort her character. Bulma is a smart scientist, and if the Vegito fanfic makes her act in a way that's not true to her intelligent and rational self, she would seem to reject it. For instance, if the fanfic has her being overly emotional or doing things that are completely against her scientific nature just to fit into a Vegito - centered plot.
It could be due to the fact that Vegito is a fusion of Goku and Vegeta. Bulma has her own relationships with these two characters separately. Her connection with Vegeta is on a more personal and family - related level, and her relationship with Goku is more of a friendship. A Vegito fanfic might create some strange or inappropriate relationships for her that she wouldn't be part of in the original story, so she rejects it.
Maybe it's because Bulma has her own established character traits and relationships in the original story. She might not fit well into the scenarios often presented in Vegito fanfic. Also, her character is more focused on other aspects like her scientific work and family in the canon, so fanfic ideas involving her in a Vegito - related context could seem out of place to her character.
One reason could be the constant threat to the world in the Dragon Ball universe. She might feel helpless as a non - fighter, seeing her friends and family in danger all the time. For example, when powerful villains like Frieza or Cell were on the loose, she could be depressed about her inability to contribute more directly to the fight.
Well, it could be that Bulma realizes that the relationship with Vegito is just too complicated or dangerous. Maybe she decides that she can't handle the chaos that often surrounds Vegito, like all the battles and threats that come with being associated with him.
In some fanfictions, Ginny may reject Harry because she wants to focus on her own personal growth. She might feel that a relationship with Harry at that time would hold her back from achieving her own goals, like becoming a great Quidditch player or an accomplished witch in her own right. So, she decides to reject him to pursue her own dreams first.
One possible reason could be stress. In fanfic scenarios, she might be under a lot of pressure from her scientific research or protecting the Earth. The stress could build up to a point where she starts to harm herself as an outlet.
To write a Bulma leaves Vegito fanfic, start with character development. Understand Bulma's and Vegito's personalities well. Maybe Bulma has grown tired of Vegito's constant battles and wants a more peaceful life. Then, build a conflict that leads to her leaving. As you write, use vivid descriptions to bring the story to life. You can include flashbacks to show the history of their relationship. And make sure to have a resolution at the end, whether it's a reconciliation or a final goodbye.
One reason could be to create a huge plot twist. It's a very unexpected and controversial idea that can immediately grab the reader's attention. Another reason might be to explore different emotional states. For example, showing how Vegeta would react to such a betrayal and how Goku would deal with the moral implications of being involved in such a situation.
One possible reason could be a radical change in Bulma's character. Maybe she's been corrupted by some dark force or has some deep - seated grudge that has been building up over time. But again, this is very uncharacteristic of her normal self.
There's a fanfic called 'Breaking Ties' where Bulma leaves Vegito. This fanfic has a unique take on their relationship and the reasons for her departure. It shows the complexity of their relationship. Some other fanfics in this category are 'Beyond the Split' which looks at the long - term effects of their separation, and 'A Solitary Choice' which focuses on Bulma's internal struggle before making the choice to leave Vegito.
It could be Frieza. He might be jealous of Vegito's power and decides to target Bulma to get to Vegito. His actions could make Bulma realize the danger she's in because of her association with Vegito, leading her to give up on him.