One possible reason could be jealousy. Maybe Naruto has achieved something great and his friends are envious. Another reason might be a misunderstanding. There could have been some false rumors or misinterpretations of Naruto's actions that led his friends to believe he wasn't trustworthy or a good friend.
It could be due to external pressures. For example, if there is some sort of threat or influence from an outside group that forces his friends to abandon him. Or perhaps Naruto has changed in some way that his friends don't understand or accept, like if he has developed new powers or a different personality trait that scares them.
One possible reason could be jealousy. If Naruto becomes too powerful too quickly, his friends might feel overshadowed and abandon him out of envy.
One possible reason could be that the writer lost inspiration. Jiraiya has a complex character in the Naruto series, and it might be difficult to keep coming up with new and interesting plotlines for him in fanfiction. Another reason could be that the writer got involved in other projects or fandoms and simply didn't have the time to continue with the Naruto fanfiction centered around Jiraiya.
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 some sort of dark influence or curse that makes her lose her maternal instincts. Maybe a powerful enemy targets her and in order to protect Naruto from further danger related to her, she feels forced to abandon him. Another reason might be that she is made to believe false information about Naruto, such as that he will bring great disaster to the village in the future.
One possible reason could be that Naruto discovers some dark secrets about the village leadership that go against his values. For example, if he finds out that they have been using underhanded means to maintain power.
Perhaps the death of a key person in his life could lead to him abandoning his dream. If someone like Iruka or Kakashi, who were important mentors to him, died in a way that made Naruto question the purpose of his dream. He might think that without their support and guidance, his dream was no longer worth pursuing.
Maybe she was forced to for some dark reason. Perhaps there was a threat to Naruto's life if she stayed, and she thought leaving was the only way to protect him.
One possible reason could be that Naruto is afraid of endangering his friends. He has many powerful enemies, and he might think that by staying away from his friends, they won't be targeted. For example, Orochimaru was always after Sasuke, and Naruto might fear that his closeness to Sasuke could put Sasuke in more danger.
One reason could be a sense of betrayal. Maybe he discovers some dark secrets about the village leadership that make him lose faith in Konohagakure. For example, if he finds out they were using him all along just as a weapon against other villages.
One possible reason could be fear. Naruto has the Nine - Tails within him, and some in Konoha might be too afraid of its power getting out of control. They may not fully trust Naruto to keep it in check.