Another reason could be to appeal to a different audience. There are people who enjoy darker, more complex stories. 'Anti social naruto fanfic' can attract those who want to see the Naruto universe from a different perspective, one that is not so rosy and full of hope. It can also be a way for writers to express their own feelings about society or human nature in a fictional Naruto - based context.
Some people write it to explore different aspects of the Naruto characters. Maybe they want to see how a character would develop if they were not bound by the social rules of the Naruto world.
Some people write anti Naruto fanfiction because they want to explore different perspectives. They might not agree with the original story's direction or the character development of Naruto. So they create their own versions to satisfy their creativity.
Another reason could be that some writers like to explore different storylines and universes. They might not be satisfied with the canon story's romantic plot and want to create their own versions. In the case of 'anti naruhina fanfic', they can rewrite the story without the Naruhina relationship and see how the story unfolds differently. This gives them creative freedom to play with the characters and the Naruto universe.
People may write it as a form of creative rebellion. The Pokemon franchise is so popular and has a very set image. By creating 'anti pokemon fanfic', they can break the mold and create something that stands out. It could also be a way for them to express their own views on things like animal rights (comparing Pokemon to animals in a sense) if they think the way Pokemon are treated in the franchise is not ideal.
Some people write anti mpreg fanfic because they prefer to stick to the traditional gender roles and biological norms represented in the original source. They might feel that mpreg is too much of a deviation from what they know and love about the characters and the story world.
Some people write 'anti Bakugou fanfic' because they don't like his aggressive and bullying nature in the original story. They want to explore scenarios where he is held accountable for his actions more than in the official plot.
People write anti - boruto fanfic because they have different ideas about how the Naruto franchise should have evolved. They may not like the new powers and abilities introduced in Boruto as they seem too overpowered or not fitting with the original Naruto's power system. Some might also write such fanfics because they feel that Boruto has overshadowed the characters they loved from the original Naruto series, and they want to bring back the focus on those characters through their fan - created stories.
Some people write it because they feel the relationship between Sasuke and Sakura was forced in the original series. They might think that Sakura could have had a better romantic option or that Sasuke was never really that into her.
Some people write 'anti Tony Stark fanfic' because they might not like his character traits. His over - confidence can come across as arrogance to some, and they want to explore the negative aspects of that in their writing.
Some people write 'bitter Naruto fanfic' to explore the darker sides of the characters. In the original Naruto series, while there are hardships, it still has a positive overall tone. By writing bitter fanfics, they can show how the characters would react in more tragic or difficult situations.