It could also be a way for writers to explore different character dynamics. By having May hurt Ash, they can dig deeper into how both characters would react in a difficult situation. For example, Ash might be more forgiving than expected, or May might feel extreme guilt. This allows for a more in - depth look at their personalities.
Another reason is that it gives the opportunity to develop new storylines. If May hurts Ash, it can set off a chain of events that might not have occurred otherwise. It could lead to new adventures, like Ash having to find a way to heal himself (physically or emotionally) and also help May deal with whatever made her act that way in the first place.
They exist because it creates drama. The relationship between Clary and Alec in the original story has a lot of potential for conflict. Writers explore different scenarios where Clary might hurt Alec, either intentionally or not, to add more depth and angst to the story.
Some exist because it adds drama to the relationship. Writers like to explore the complex emotions and conflicts that can arise between two very different characters like Vegeta and Bulma.
Some writers might be exploring the darker side of human nature. Gale is a complex character. He has his own desires and goals. In the context of the story, his actions could be misinterpreted or could genuinely cause harm to Katniss. Fanfiction allows for a deeper dive into these possible scenarios, showing how even a character like Gale, who has good intentions at times, can still end up hurting the person he cares about.
One popular 'May Hurts Ash' fanfiction could be about a misunderstanding between them that leads to emotional turmoil. For example, May might accidentally damage Ash's important Pokémon item during a competition preparation, causing a rift in their friendship.
Some 'Harry Hurts Ginny' fanfics exist because it adds a new layer of drama to their relationship. Their relationship in the original series was mostly positive, but exploring the negative aspects like Harry hurting Ginny can make for an interesting and complex story.
Some exist to explore darker themes. Writers might want to show the resilience of a character like Frisk in the face of extreme adversity. For example, by having Frisk go through abuse, they can then show how Frisk overcomes it and grows as a character.
Some exist because it creates a really intense and dramatic conflict. Bellatrix is a very powerful and cruel character, and Hermione is a strong - willed heroine. Putting them in a situation where Bellatrix tries to break Hermione makes for a very engaging read.
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.
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 exist because fans like to explore different power dynamics in relationships. They want to see how Harry, as a central and powerful character, can influence Ginny's actions and decisions.