Perhaps the village's strict rules and regulations are getting on his nerves. He has always been a bit of a rebel at heart, and constantly having to abide by the village's ways could make him fed up. For example, if the village restricts his ability to use certain jutsus or interact with certain people, it could lead to his frustration.
One reason could be the lack of recognition he gets in the village despite his great contributions. In the fanfiction, Naruto might feel that his efforts to protect the village are taken for granted.
It could also be that he's tired of the politics in the village. There might be power - hungry individuals or groups in the village who are constantly causing trouble and Naruto has had enough of dealing with them. He might feel that the village is more focused on power plays rather than the well - being of its people.
Perhaps Naruto is fed up with Konoha's fanfiction because he wants a new adventure outside of the village. He has spent most of his life in Konoha and might be craving for a change. He could be bored with the same old politics and power struggles within the village. Also, he may have realized that the ideals of Konoha are not as perfect as they seem, and this disillusionment makes him tired of it.
Well, it might be that the fanfiction focuses too much on Sakura in a way that Naruto feels is unfair to the other characters. Naruto is part of a big world with many important people, and if the fanfic just hones in on Sakura all the time, he could get fed up. Also, if the fanfiction has Sakura constantly putting Naruto down or not appreciating his efforts like in the real story, that could be a reason.
One reason could be that in some fanfictions, the characters of Team 7 are portrayed out of character. Naruto might be fed up if they make Sasuke too brooding in a way that doesn't seem true to the original. Also, if the fanfiction focuses too much on shipping within Team 7, like Sasuke and Sakura, and ignores Naruto's growth and importance, it could annoy him. Another possibility is if the fanfiction makes the team seem too dysfunctional in a way that doesn't match Naruto's view of his comrades.
Perhaps the fanfiction keeps rehashing the same tired storylines about Konoha. Naruto might be tired of seeing the same things over and over again, like always focusing on the village's dark secrets in a clichéd way instead of exploring new aspects of Konoha and its people.
He could start to oppose the village's leadership more openly. Instead of being the village's hero who always follows orders, he might become a vocal critic. He might use his influence among the villagers to try and bring about change in the way the village is run. For instance, if he thinks the village is being too harsh on the younger generation of ninjas, he could start a movement to change the training methods.
It could be due to Dumbledore's decisions regarding Harry. Sirius is very protective of Harry. If he thinks Dumbledore is using Harry in some way for the greater good without fully considering Harry's well - being, he would be fed up. For instance, Dumbledore's decisions about Harry's participation in the Triwizard Tournament could be a point of contention for Sirius.
Maybe it's to protect the village. He could discover a threat that he can only face away from the Leaf Village, to keep the danger from directly reaching his home and loved ones. He leaves as a form of self - sacrifice.
Sometimes, the plotlines in fanfiction can be a bit outlandish. If Ron is constantly getting into trouble in a way that Hermione has to constantly clean up after him, it would be understandable for her to be fed up. This could be different from the more equal partnership they had in the original series.
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.
One possible reason could be that he feels misunderstood. In the village, he has always faced discrimination because of the Nine - Tails inside him. People often look at him with fear and suspicion. So, he might run away to find a place where he can be accepted for who he is.