It could also be due to a threat to his loved ones. If the village is unable or unwilling to protect his friends or family, Naruto might see defecting as the only way to keep them safe. He has always been very protective, and if Konoha fails in this regard, he may choose to leave.
Another reason might be a lack of acceptance. Despite all his efforts, if Naruto still feels like an outcast in Konoha, he could decide to defect. He might think that he can find a place where he is truly understood and valued elsewhere.
He could defect because of a false accusation. For example, if he is wrongly blamed for a serious crime in the village. This would make him feel betrayed and unwanted. Also, if someone he deeply trusts in Konoha turns against him, it might push him to leave. It's not easy for Naruto, who has always yearned for acceptance in Konoha, but such circumstances could drive him away.
Perhaps he discovers something about his past or his powers that makes him feel he has to leave Konoha to explore it further. For example, he might find out about a hidden place related to the Uzumaki clan and wants to go there alone to uncover the secrets. Or it could be that he has some kind of internal conflict within himself, like feeling unworthy of being in Konoha due to some self - perceived failure, and so he runs away.
Maybe it's due to a misrepresentation of Naruto's character. In the official Naruto series, he is a hero who is deeply connected to Konoha. If the fanfiction shows him in a negative light without proper justification, like suddenly turning against Konoha for no good reason, it could be banned. Also, if the fanfiction involves some sort of political incorrectness within the context of the Naruto universe, such as discriminatory ideas towards certain clans in Konoha, that would be a reason for a ban.
It would also create a power vacuum. Naruto was a strong force in Konoha. Without him, the village would be more vulnerable to attacks. Enemies might take advantage of the situation, leading to a whole new set of challenges for Konoha.
One reason could be that he feels misunderstood by the villagers. Despite all he has done for Konoha, some still hold grudges or are afraid of his power. Another might be that he wants to explore the world on his own terms, away from the responsibilities and restrictions of Konoha. Maybe he also feels a sense of loneliness there, as he has lost many important people and the village constantly reminds him of those losses.
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.
One possible reason could be false accusations of a serious crime. For example, if he was wrongly blamed for a major attack on the village. Another reason might be political intrigue. Some powerful figures in the village might see Naruto as a threat to their power and find a way to banish him to maintain their control.
Another reason could be for the sake of protecting the village. Maybe he discovers some sort of threat that he believes he can only face by leaving Konoha. He doesn't want the village to be in danger because of him, so he runs away to draw the danger away from Konoha.
In fanfiction, it could be due to a new threat that Konoha refuses to take seriously. Suppose there's a new and extremely dangerous enemy on the rise, and Konoha's leadership decides to ignore it or handle it in a way Naruto and Sasuke don't agree with. They might then choose to leave Konoha to face this threat on their own terms, believing that they can't do it while being restricted by Konoha's rules.
One reason could be false accusations. Maybe some powerful individuals in Konoha frame Naruto for a serious crime he didn't commit. For example, they could plant evidence that he was involved in a plot against the village leaders. Another reason might be the fear of his power. If his strength grows too rapidly and uncontrollably in the fanfiction, the elders or some conservative forces in Konoha may decide to exile him to prevent any potential disasters. Also, political intrigue could play a part. If there are different factions vying for power in Konoha and Naruto becomes an obstacle or a scapegoat for one of them, they could manipulate the situation to get him exiled.