One possible reason could be that he experiences a great personal loss. Maybe he loses someone very dear to him during a mission, like his best friend or a respected mentor. This loss makes him question the whole ninja life and all the violence and danger it entails, leading him to give it up.
One possible reason could be that he experiences a great loss, like the death of a dear friend. This might shatter his confidence and make him lose his passion for being a ninja.
It could be due to a physical or mental injury. If Naruto got seriously injured during the Chunin Exam, and he didn't think he could recover in time to compete effectively, he might give up. Mentally, if he was somehow affected by a genjutsu that made him lose his confidence or will to fight, that could also lead to his decision to give up.
One reason could be the overwhelming pressure. Being Hokage means shouldering the safety and well - being of the entire village. Naruto might have realized that he can't bear that kind of stress forever. Another factor could be personal sacrifice. He may have seen how being Hokage has cost others in their personal lives and he doesn't want to go through the same. Also, he might have new dreams or goals that are not compatible with the role of Hokage, like exploring the world outside the village more freely.
In some cases, the fanfiction might be a crossover with another universe where the idea of a ninja doesn't fit. So, to make Naruto fit into this new universe, the writer has to take away his ninja identity. This allows for new and interesting interactions between Naruto and characters from the other universe.
It could be that Naruto has other creative or intellectual interests. For example, he might be more interested in art or learning about the history of the ninja villages rather than participating in ninja battles. He could find the rigid ninja training and the constant competition unappealing. Also, perhaps he has a different sense of purpose, like wanting to focus on building peace in a non - combat way, which doesn't require being a ninja in the traditional sense.
One possible reason could be to protect his friends. He might think that by sacrificing his heart, some great danger or enemy would be vanquished, thus ensuring the safety of those he cares about. For example, if there was a powerful curse that could only be broken by his heart's sacrifice.
It could also be that he is tired of the false expectations created by fanfiction. In fanfiction, his character might be portrayed in ways that don't match who he really is. He wants to be true to himself and his ninja way, so he gives up fanfiction.
Maybe Naruto gets tired of always chasing after Sasuke. He has his own life and dreams too. He might think that he has sacrificed enough of his time and energy on Sasuke, and it's time to focus on himself and the village. He could start to believe that Sasuke has made his own choices and he can't keep forcing Sasuke to come back.
One possible reason could be that he gets tired of the constant fighting and bloodshed. He might have seen too many friends get hurt or die, and it just becomes too much for him to bear. Another reason could be that he discovers a new purpose in life outside of being a ninja, like focusing on family or helping the village in a non - combat way.
It could also be due to a misunderstanding. Some false information might have spread in the fanfic's world, making Naruto believe that everyone has turned their backs on him. Like, some bad guys framed his friends, and Naruto, being unable to see through the lies at first, gives up on everyone in despair.