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.
It could also be related to a new power or ability he has discovered. He might think that he can handle things on his own better with this new power and doesn't need the support of Team 7. For example, if he has unlocked a new form of his chakra that gives him extraordinary strength, he may become overconfident and start ignoring his team.
Maybe he got some kind of curse. In the Naruto universe, there are all sorts of dark magic and curses. If he was cursed, it could make him withdrawn and cause him to ignore everyone.
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.
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.
In some fanfictions, Naruto could be mad at Team 7 if there was a new member added and he felt replaced. He has a deep bond with Sasuke, Sakura, and Kakashi, and any disruption to that dynamic might lead to anger. Also, if the team made a decision without consulting him, like choosing a mission target without his input, that could be a cause for his anger.
Another reason could be the lack of trust he feels from his teammates in some fanfiction scenarios. If Sasuke is constantly keeping secrets or Sakura is doubting Naruto's abilities, it can make him feel isolated within the team and eventually tired of being part of it.
One reason could be that Naruto has his own independent goals. He's always been determined to become Hokage. Maybe the team's goals don't align with his. For example, if the team is more focused on short - term missions for money rather than long - term village development like Naruto wants.
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 plot device to create drama. Maybe the author wants to show a rift between them for the sake of a more complex storyline. For example, if there's some misunderstanding or a secret that has come to light which makes Harry act this way.
One possible reason could be a sense of being too powerful and outgrowing the team. If Naruto in the fanfiction has become 'godlike', he might feel that the training and missions of Team 7 are no longer challenging enough for him. He may seek greater challenges elsewhere.