Perhaps Naruto is framed for a crime he didn't commit. The villagers, quick to believe the false accusations, turn against him. Feeling betrayed by the very people he once swore to protect, he then decides to betray Konoha in return. For example, if he was wrongly accused of assassinating an important figure in the village.
Another scenario could be that an outside force, like a powerful enemy, convinces Naruto that Konoha is not worth protecting. They might show him a vision of a future where Konoha becomes a tyrannical regime or is responsible for mass destruction. This could sway Naruto's loyalty and lead him to betray the village.
One possible reason could be that Naruto discovers some dark secrets within Konoha. Maybe he finds out that the village elders have been using him all along, not truly caring about his well - being but only his power as a Jinchuriki. This realization could be so shocking that he decides to turn against the village.
One possible plot could be that Naruto discovers some dark secrets about Konoha's leadership. For example, he might find out that they were involved in unethical experiments in the past. This discovery could make him feel betrayed first, and then lead him to take actions that Konoha sees as betrayal, like refusing to follow orders or even teaming up with an enemy of Konoha who he believes has a more just cause.
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 reason could be betrayal. If Naruto discovers that some in Konoha have been secretly plotting against him or have been involved in something immoral that goes against his values, he might forsake the village. For example, if there was a conspiracy to keep him from achieving his true potential for their own gains.
One possible reason could be fear. Naruto is extremely powerful, and some in Konoha might fear that he could one day lose control of his power. Another reason could be political intrigue. There may be certain factions within Konoha that see Naruto as a threat to their power and influence. Also, jealousy might play a part. Naruto has achieved so much and has the love of many, and some might be jealous and thus plot against him.
Perhaps the Konoha leadership made a bad decision. They might have thought that distancing themselves from Naruto would be better for the village's overall image. Or they were influenced by some elders who held grudges against Naruto's father and took it out on Naruto.
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.
Another reason could be that he witnesses corruption or unfairness within the village leadership. If he sees that the system is rigged against certain groups, including himself or his friends, he could grow to hate Konoha and decide to leave.
Well, in the fanfiction, perhaps Naruto realizes that Konoha's politics are too complex. There are always hidden agendas and power plays. He, being a straightforward person, might get tired of all the behind - the - scenes stuff. Also, he may feel that his friends are changing because of Konoha's influence. For example, they might be more focused on the village's reputation rather than their true feelings, which makes Naruto sick of it all.
The Konoha elders could be the main antagonists. They are often shown to be quite traditional and set in their ways in the original series. If Naruto goes against their old - fashioned ideas about the village's future and ninja code, they would likely oppose him strongly and could be the driving force behind making Naruto an outcast, which in turn could lead to his 'betrayal'.
One possible reason could be feeling betrayed by the village leaders. Maybe they made decisions that Naruto strongly disagreed with, like how they treated certain groups or individuals. If Naruto felt that Konoha was no longer the place that stood for justice and fairness as he once believed, he might abandon it.