In some fanfictions, the world - building might be different. There could be a new political situation in the village. If Jiraiya takes a side that Naruto believes is against the well - being of the village or his friends, Naruto may start to hate him. Also, if Jiraiya is somehow responsible for the harm of someone close to Naruto in the fan - created story, that would definitely make Naruto hate him.
One possible reason could be jealousy. Maybe in the fanfiction, Jiraiya gives more attention to another character, and Naruto, being young and impulsive, starts to hate him for it.
He may dislike it because he feels that it undermines the real struggles and achievements of the ninja. In fanfiction, things might be made too easy or unrealistic. He has fought tooth and nail for everything in his ninja life, and seeing it made into something that doesn't represent that in fanfiction would make him hate it.
One reason could be jealousy. If in the fanfic, Sakura gets closer to someone else Naruto cares about, like Sasuke in a different way than he expected, it might make him hate her. For example, if Sakura teams up with Sasuke against Naruto's wishes in the fan - created plot.
Perhaps he has seen fanfiction that contains inaccurate information about the Naruto universe, such as wrong jutsu descriptions or incorrect interpretations of the ninja clans. This would make him dislike it as he is an educator in the Naruto world and has a certain standard for knowledge about it.
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.
One possible reason could be that Naruto feels he has learned all he can from Jiraiya at that point. Maybe he has reached a level in his training where he believes he needs new experiences and challenges that Jiraiya can no longer provide.
One possible reason is a misunderstanding. If there are rumors or false memories planted in Naruto's mind, he might believe his mom did something unforgivable. For instance, if he's made to think she was involved in the death of someone he cared about.
One possible reason could be that Naruto feels he has learned all he can from Jiraiya at that point. Maybe he wants to explore his own path independently and test his skills without Jiraiya's constant guidance.
In some fanfics, there could be a misunderstanding. Suppose Kushina did something that Naruto misinterpreted as harmful to him or his friends. This misinterpretation could lead to his hatred. For example, if Kushina was involved in a mission that Naruto thought put the village at risk, but in reality, she had no choice.
One possible reason is that the person may find the fan - made interpretations of the Pokemon world too far - fetched. For example, some fanfictions might give Pokemon abilities that are completely against the established rules in the official games or anime. This can be off - putting to those who like the consistency of the official lore.
Some writers might want to create a unique or controversial take. They think by bashing a well - liked character like Jiraiya, they can attract more attention to their fanfiction.