Well, in the world of 'anti sasusaku fanfic', a lot of it has to do with fan dissatisfaction. Fans who write these may feel that the SasuSaku relationship was forced or not well - developed. Some works might be a way to explore what could have happened if Sasuke had made different choices regarding his relationships. For instance, a fanfic could show Sasuke choosing a life of solitude instead of getting involved with Sakura. This gives the writers a chance to play with the characters' personalities and the overall story arc in a way that goes against the canon SasuSaku relationship.
There are several 'anti sasusaku fanfic' works out there. The existence of these can be due to the fact that different fans have different interpretations of the characters. Some might see Sasuke as being better suited to a more independent or less emotional relationship. These fanfics may focus on highlighting the flaws in the SasuSaku relationship as presented in the official story. They might rewrite the story to have Sasuke reject Sakura in a more permanent way and explore how the characters would develop from there.
One possible 'anti Sansa fanfic' might be written because some people dislike her character development in the original story. Maybe they think she's too naive at times. However, this is a very subjective view as many others love her character.
Anti Sasusaku fanfic focuses on going against the Sasusaku relationship. So, while regular Sasusaku fanfic might show the growth and love between Sasuke and Sakura, anti ones would show the opposite. For example, they could show Sasuke constantly rejecting Sakura or having a negative view of her.
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.
One reason is that they might be following old - fashioned ideas. Some authors may be influenced by traditional gender roles from the past and unconsciously write stories that are anti - feminist. Also, they could be trying to target a specific audience who still holds such views.
I'm not really sure which specific 'female Sora Riku anti fanfic' works are out there. It could be hard to find them as they might not be very mainstream. Maybe you could start by looking in some niche fanfic communities or forums dedicated to the source material where Sora and Riku are from.
One reason is to add some drama. In the Naruto story, Sakura and Naruto have a long - standing relationship. A slap can create an instant moment of tension. It can also be a way to show Sakura's strong personality. She's not one to hold back her emotions, and a slap can be a very physical way of expressing her feelings, whether it's anger or frustration.
Some writers create these fanfics because it allows them to explore different character dynamics. When Voldemort cheats, it shows his desperation or his devious nature in a new light. And it also gives Harry a different kind of challenge to overcome, not just a physical or magical one but also a moral and strategic one. For example, if Voldemort cheats by bribing people around Harry, Harry has to decide how to deal with those who have been turned against him, whether to forgive or fight back.
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.