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.
Maybe Naruto has seen too many unrealistic or out - of - character portrayals of Konoha in the fanfiction. For example, some might make Konoha overly cruel or its people too stupid, which goes against his understanding and love for his village.
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 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 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.
In fanfiction, Naruto could feel sick due to overusing his chakra. He often pushes himself to the limit in battles and training, and this excessive chakra use might take a toll on his body, making him feel ill.
Maybe he's tired of the same old dynamics. In fanfiction, sometimes the relationships in Team 7 can be written in a very repetitive way. For example, Sasuke's brooding and Sakura's one - sided love for Sasuke can become overdone, making Naruto feel sick of it all. Also, if the fanfiction focuses too much on the team's conflicts without any real development, it could be a reason.