Some writers do it to explore the darker aspects of their relationship. Sasuke has a complex personality and his past traumas could potentially lead him to do such things. It's a way to dig deeper into the characters and see how they would react in extreme situations.
One reason is to create a sense of conflict. Conflict is the essence of a good story. Sasuke and Sakura have a complex relationship in the original work, and by pushing it to such an extreme in fanfiction, writers can show how love, hate, and forgiveness can all play out. It also allows for character development as both Sasuke and Sakura are forced to face their own demons and each other's in a very intense way.
Another reason might be to subvert the expected. In the original story, there's a certain expectation of their relationship. By having Sasuke dump Sakura, writers can create unique and unexpected story arcs. They can introduce new love interests for Sakura or explore different directions for Sasuke's character development that might not have been possible if the relationship had continued as expected.
Writers might be interested in exploring the idea of independence. Sakura has often been in the shadow of other characters. When Kakashi leaves, it gives her the opportunity to step out and shine on her own. It can also lead to new relationships and alliances for Sakura that she might not have formed if Kakashi had stayed. For example, she could form a closer bond with other members of her team or with characters from other villages.
It could be a way to explore different character developments. By having Sasuke cheat, the writer can show a different side of Sakura, perhaps a stronger and more independent side as she deals with the betrayal. Also, it allows for a deeper exploration of Sasuke's character, maybe he has some hidden flaws or temptations that lead to this situation.
Some writers might do it to explore the darker side of human nature and raise awareness about certain issues.
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.
One reason could be to add drama. By having Naruto hurt Sakura, it creates conflict which is a key element in storytelling. It can make the plot more interesting and engaging as it forces other characters to react and deal with the situation.
Well, some writers might portray Sasuke as more vulnerable in fanfiction than in the original series. They could show him relying on Sakura more for emotional support. For example, after a difficult mission, he might seek Sakura's comfort instead of shutting her out. On the other hand, Sakura could be depicted as even more assertive. Instead of just pining for Sasuke, she could be the one to take the lead in their relationship, making decisions about their future together.
Some people write it because they may not like the canon relationship between Sasuke and Sakura. Maybe they preferred Sasuke with another character or just didn't like how their relationship developed in the original story. They use fanfiction as a way to explore their own ideas of what could have been different.
Some people might write Sasuke and Sakura cheating fanfiction because they want to explore alternative storylines. Maybe they are tired of the traditional, positive relationship portrayal and want to see what would happen if there was some drama or conflict in their relationship in a very extreme way.
Some people write it because they want to see a different side of Sakura. They might be tired of the typical Sasuke - Sakura relationship in the original series and want to explore what would happen if she had the agency to reject him.