Well, one reason could be that Hinata's extreme love for Naruto gets out of hand. In the original series, she's very shy but deeply in love. In a fanfiction, this love could transform into an obsessive - like stalking behavior if the writer wants to explore a darker side of her character.
In a 'Naruto is stalked by Hinata' fanfiction, the reasons could be multi - faceted. It could be related to her clan's pressure. Maybe the Hyuga clan wants her to be closer to Naruto for some political or strategic reasons, and she goes about it in the wrong way, like stalking. Or it could be that she has some insecurities about losing Naruto to other girls, especially considering how popular he is. This insecurity could make her overstep boundaries and start stalking him to ensure he stays within her reach. Also, it could be a creative way for the author to explore the concept of an unbalanced or 'toxic' form of love in the Naruto universe.
One possible reason could be a huge misunderstanding. Maybe he thought Hinata did something really bad to his friends, like unknowingly leading the enemy to them. Without knowing the truth, his hot - headed nature made him lash out.
It could be due to miscommunication. Suppose there was a misunderstanding between her and Naruto. For example, Naruto might have said something that Hinata misinterpreted as him losing interest in their relationship. This confusion could have led her to seek comfort in another person, which unfortunately led to cheating.
One possible reason could be that Naruto has a dangerous mission that only he can undertake. The safety of the village or the greater good might demand his immediate departure, even though it's hard for him to leave Hinata in such a state.
One possible reason could be a misunderstanding. Maybe some false information is spread about Hinata that makes Naruto believe she has done something unforgivable. For example, if there's a plot to frame her for treason against the village. Another reason might be for her own safety. Naruto might think that banishing her would keep her away from a greater danger that is targeting her because of her relation to him.
One possible reason could be a misunderstanding. Maybe Hinata is misinformed about Naruto's actions or intentions. For example, she might be led to believe that Naruto has done something harmful to the village when in fact he's innocent.
One reason could be envy. Maybe Naruto sees Hinata as having something he doesn't, like a more stable family situation, and he lashes out in jealousy. Another reason might be that he's just being a typical, rambunctious kid who doesn't realize the impact of his words or actions on Hinata.
In some fanfictions, external forces might be the cause. Perhaps a powerful enemy threatens Hinata and tells her that staying with Naruto will put him in danger. So, to protect Naruto, she decides to abandon him. This adds a tragic and self - sacrificing element to the story.
One possible reason could be a misunderstanding. Maybe Naruto was in a situation where it looked like he was cheating, but in reality, it was all a big mix - up. Another reason could be that the writer of the fanfiction wants to explore a darker side of Naruto's character. Or perhaps there's some sort of outside influence, like an enemy using some kind of mind - control on Naruto to make him act out of character.
A simple reason could be that they are poisoned. An enemy might have laced their food or drink with a slow - acting poison that causes them to faint at an unexpected moment.
In certain fanfictions, Naruto might have a pre - existing relationship or unrequited love for someone else. This could make him overlook Hinata or even seem to dislike her because his heart is set on another character.