Perhaps Naruto quits Team 7 in the fanfiction because of a betrayal. He might find out that one of his teammates has been secretly working against him or has lied to him about something really important. This could shatter his trust in the team and make him want to leave. Or it could be due to an accumulation of small incidents. Like constantly being the one to get in trouble for the team's mistakes, or not having his opinions heard when it comes to team strategies. Over time, these little things can build up and make him feel that he's better off on his own.
One reason could be a sense of not being understood. Maybe Naruto feels like his teammates, Sasuke and Sakura, don't truly get him. Sasuke is often preoccupied with his own revenge, and Sakura has her eyes mainly on Sasuke. Naruto might feel left out and that his goals are not aligned with the team's, so he decides to quit.
It could also be due to a major disagreement with Kakashi. Maybe Naruto has a different vision for how they should operate as a team or a particular mission that goes against his values, causing him to leave.
One possible reason could be a sense of being undervalued. Maybe he felt that his teammates didn't fully appreciate his efforts during the Wave mission. For example, if Sasuke got most of the credit, Naruto might feel pushed aside.
It might be due to a lack of inspiration. Writing fanfiction requires continuous creativity, and if they ran out of new ideas related to Naruto and the ninja world, they could decide to quit. For example, they might have explored all the character arcs and plotlines they could think of within that context.
One possible reason could be that Naruto realizes the Chunin Exams have become too dangerous and he doesn't want to risk his life or the lives of his friends. Maybe he sees the dark side of the competition, like how some contestants are willing to cheat or harm others to win.
Perhaps an injury could cause him to quit. If he gets seriously hurt in one of the early rounds and realizes that continuing could lead to permanent damage or even death, Naruto might choose to step down. He's brave, but not foolish. He also has dreams of becoming Hokage and if he thinks that by continuing in the Chunin Exams in an injured state he could jeopardize his long - term goal, he would rather quit and live to fight another day.
It could also be due to personal growth. Naruto might have outgrown the ideals and limitations of being a Konoha ninja. He may have developed his own set of values that no longer align with the village's ninja system. For example, he could have found that the constant focus on missions and loyalty to the village overshadowed the importance of individual freedom and justice on a broader scale.
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.
One possible reason could be miscommunication. Maybe Naruto misunderstands something Team 7 members say or do. For example, if they seem to be excluding him from a plan without a good explanation. Another reason might be stress. Naruto has a lot on his plate, and if Team 7 accidentally adds to his burden in the fanfiction, he could snap. Also, personal growth differences. If Naruto is growing in a different direction than the rest of Team 7 and they don't understand or support him, it could lead to him snapping at them.
Perhaps Naruto is being influenced by an outside force. It could be an enemy who has tricked him into believing that his team is holding him back. Or it could be that he has fallen into a dark state of mind, like if he has some kind of mental breakdown due to all the pressure he has faced in the past. In this state, he might just push Team 7 away without really meaning to in the long run.