It could also be due to personal growth. Naruto might have outgrown the ideals and limitations of being a Konoha ninja. He may have developed his own set of values that no longer align with the village's ninja system. For example, he could have found that the constant focus on missions and loyalty to the village overshadowed the importance of individual freedom and justice on a broader scale.
For Sasuke, it could be a complex reaction. He has his own issues with Konoha, but Naruto was always a sort of anchor for him. Naruto leaving could either push him further away from the village or make him re - evaluate his own relationship with it.
The story's focus would change completely. Instead of action - packed ninja battles, it could turn into a more character - driven plot about Naruto's new life. Maybe he starts a family or a business. His relationships with other characters would also change. His friends who were used to fighting alongside him would now have to interact with him in a different context, like when he's just an ordinary citizen.
It might be due to a lack of inspiration. Writing fanfiction requires continuous creativity, and if they ran out of new ideas related to Naruto and the ninja world, they could decide to quit. For example, they might have explored all the character arcs and plotlines they could think of within that context.
It might inspire other writers in the community. Some might see it as an opportunity to fill the gap and start creating their own unique takes on Naruto - related stories. For example, new writers could emerge trying to recreate the kind of stories the 'quitting' writer used to write.
I really like 'Konoha's Hidden Power'. In this fanfic, it shows how different ninja in Konoha discover new powers. It's full of action and adventure, with the characters facing tough challenges that make for an exciting read.
One possible fanfiction could be about Naruto's heroic deeds finally making the entire Konoha truly love and accept him unconditionally. For example, after saving the village multiple times from powerful enemies, the villagers start to see him not just as the container of the Nine - Tails, but as a true hero. They hold grand celebrations in his honor and every citizen looks up to him with pride.
There would be a group of people who understand his decision. They might have seen how much Naruto has sacrificed and how tired he must be. They would support him in his choice to step down and hope he can finally have some peace in his life. For instance, his close friends like Shikamaru might be among those who support his decision.
The storyline would be completely different. Naruto's character development would take a new turn. He would no longer have the instant boost of power from the Nine - Tails. This might make him more vulnerable, but also force him to rely more on his own skills and training. His interactions with the other Jinchuuriki would also change. They might view him as a traitor to their kind or as a pioneer for a new way of living without the tailed beasts.
One possible plot twist could be that Naruto discovers a new power source that makes being a Jinchuuriki seem obsolete. Maybe he finds an ancient artifact or a new form of chakra that is more powerful and doesn't have the drawbacks of being a Jinchuuriki. Another could be that he has a moral dilemma about the nature of the Jinchuuriki system and decides to quit in protest. For example, if he realizes that the Jinchuuriki are being used as tools more than protectors.