Another reason could be for shock value. By creating a scenario where Sasuke abuses Naruto, the writers can attract readers who are interested in seeing unexpected and controversial plot twists. But this kind of fanfiction often goes against the general spirit of the original Naruto series which focuses on friendship, growth, and redemption.
Some people write it to explore the darker side of the Naruto - Sasuke relationship. They want to see how the characters would react in extreme situations that are different from the main storyline.
Another reason could be that some fans are so strongly attached to Naruto that they view any character who they think treats Naruto poorly as a target for criticism in fanfiction. Sakura, at times, did seem to take Naruto for granted in the original story. So, these fans write fanfictions to express their dissatisfaction with her character. Also, it could be a creative outlet for those who want to explore a different dynamic between Naruto and Sakura, one where Naruto is more assertive against her perceived flaws.
It could also be a way to explore alternative storylines. For example, if Sakura rejects Naruto, it can open up new paths for both characters. Naruto might have to find love elsewhere or focus more on his Hokage dreams without the distraction of a romantic relationship. And for Sakura, it can show her independence and her own journey of self - discovery outside of a relationship with Naruto.
The existence of Naruto abandoned crossover fanfictions can also be due to the difficulty of maintaining consistency. In a crossover, not only do you have to keep the Naruto universe rules intact, but also those of the other universe. For example, in a Naruto and 'Fullmetal Alchemist' crossover, the author has to make sure that the laws of equivalent exchange in 'Fullmetal Alchemist' don't conflict with Naruto's power - up systems. If it becomes too much of a headache to keep everything in order, the author may just drop the fanfiction.
These fanfictions exist because many fans like to explore alternative storylines. The idea of Naruto being banished adds a lot of drama and conflict to the story. Hinata's relationship with Naruto in these scenarios allows for a deeper exploration of her character, especially her loyalty and love for Naruto.
Some people write them because they see a deep and complex relationship between Sasuke and Naruto in the original series. The idea of a romantic connection between them is an interesting exploration of the characters' bond that wasn't fully realized in the canon.
Well, in the Naruto series, Sakura has a strong connection to Sasuke. Fanfiction writers create 'sakura dies for sasuke' stories to add a new dimension to their relationship. It could be a way to show how far Sakura would go for Sasuke, highlighting her loyalty and love. Also, it might be used to create a more tragic or angsty storyline, which some readers really enjoy as it adds more drama to the existing Naruto narrative.
It could be that the writers are exploring power dynamics in a very extreme way. Maybe they misinterpreted the complex relationship between Naruto and Sasuke. In the original, they have a balance of power, but these writers might be trying to create a situation where one has complete control over the other for the sake of a unique story, although it's not in line with the original spirit. Another reason could be that they just want to write something controversial to generate discussion among fans.
Another reason could be to deviate from the original story's narrative. In the original, they have a lot of attention in different ways. By making them neglected, it creates a whole new set of plot possibilities. For example, they might form different alliances or develop new skills out of necessity.
It could also be to add more depth to their relationship. When they are neglected, they have to rely on each other more. For example, in a fanfiction where the village turns their backs on them, Naruto and Sasuke might form an even stronger bond as they face this together. This gives writers a chance to develop their friendship in new and interesting ways. Also, it can be a way to introduce new plotlines and conflicts that wouldn't exist in the original story. By changing their status from being in the center of attention to being neglected, new challenges and opportunities for character growth are created.