Some fans might write this type of fanfiction as a form of catharsis. They may have had certain emotions or ideas related to the characters that they want to express in a more extreme way. Also, it could be a way to explore the moral and ethical boundaries within the Percy Jackson world. By having Annabeth torture Percy, it forces the readers and the writer to think about what is right and wrong in that fictional context, and how the characters would be affected by such actions.
Some people might create it out of a desire to explore dark or 'what - if' scenarios that are completely opposite to the normal relationship in the original work. It could also be a way for them to experiment with different types of conflict in writing, though it's not a very positive or healthy way.
It could be that the writer wants to explore the darker side of human nature within the context of these characters. By having Annabeth cheat with Zeus, they can delve into themes like betrayal, jealousy, and the breakdown of relationships. Additionally, some might be doing it as a form of rebellion against the 'perfect' relationship that Annabeth and Percy seem to have in the original, wanting to add a bit of chaos and realism to the fictional world.
One reason could be for shock value. Writers might want to create something completely different from the normal, loving relationship in the Twilight series to get a strong reaction from readers. Another possibility is that they want to explore the darker sides of the characters, pushing the boundaries of what we know about Bella and Edward.
It could also be that in the fanfiction, Percy is given a new power or ability that Annabeth sees as a threat. Or perhaps Percy is made to side with someone Annabeth dislikes, causing her to 'hate' him in that fan - created story. This shows how different plot elements in fanfiction can change the dynamics between characters.
Perhaps the fanfiction is set in an alternate universe where something has happened to change Percy's feelings towards Annabeth. For example, if there was a betrayal in the fan - created story that made Percy turn against her.
Well, one possible reason could be that Percy made a really stupid decision without consulting Annabeth first. Like, if he went off on a dangerous mission on his own when they were supposed to be a team. Annabeth is a very strategic person and she might feel betrayed or extremely frustrated by such actions.
It could also be due to some sort of magic or mind - control. A powerful enemy might have cast a spell on Annabeth, forcing her to turn against Percy. In this case, it's not really her own will but the result of external manipulation.
Love is a big reason. She loves Percy deeply and is afraid of losing him. In the world of the fanfiction, there could be many threats to their relationship, so she holds on tightly.
One possible reason could be her deep love for Percy. She might see his life as more valuable in the grand scheme of things, perhaps because of a prophecy or a mission that only he can complete. So, she chooses to sacrifice herself to ensure his survival.
Some writers might create 'percy tortured fanfic' to shock the readers. It's a way to get a strong reaction and stand out in the vast sea of fanfiction. They might think that by presenting such a disturbing scenario, they can engage readers who are looking for something different from the typical happy - go - lucky fanfic.