Perhaps she realizes that the shinobi world is full of politics and corruption. She may not want to be part of a system that is more concerned with power plays than the well - being of its people, so she decides to quit.
She could also quit for personal reasons like wanting to focus on her family or other aspects of her life. After spending so much time as a shinobi, she may feel she has neglected other important things and decides it's time to step away.
One reason could be that she might have faced too much trauma from battles. Constant fighting, seeing friends get hurt or die, could have taken a toll on her mental health, leading her to quit.
Maybe he realizes that the shinobi world is too corrupt. There could be political intrigue and power struggles that go against his ideals. He has always fought for peace and unity, but if he sees that the system is beyond repair, he might choose to quit. Also, he could have a family situation that requires him to step away from the shinobi life. For instance, if he has a child with special needs that demands his full attention.
One reason could be that he was treated unfairly by other shinobi. If he was constantly looked down upon or discriminated against by his fellow shinobi, it might make him develop a hatred for them.
One reason could be the excessive toll on his personal life. He might have realized that being a shinobi means constantly sacrificing his time with family and friends. For example, he missed out on important moments in his son's life. Another reason could be disillusionment with the shinobi system. He may have seen the corruption or the never - ending cycle of violence within it and decided he no longer wanted to be part of it.
One reason could be to explore a different side of Naruto's character. In the original series, he's so warm - hearted, but by making him cold and distant, the writer can show how different events could have shaped him in an alternate way. Maybe he faced more hardships or betrayals that led to this change.
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.
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.
Perhaps there is some external threat or danger related to Quidditch. Maybe there is a dark wizard who is targeting Quidditch players and Harry doesn't want to put himself or his friends in danger. He has already faced so many threats in his life that this additional risk related to Quidditch might be too much for him.
One possible reason could be the overwhelming loss he has faced. He's lost many dear friends and mentors throughout his journey. For example, when Jiraiya died, it was a huge blow to him. Another reason might be the constant pressure of being the savior of the village. The weight of everyone's expectations could lead him to feel so tired and defeated that he gives up on life.
One possible reason could be that the writers lost interest in the Harry Potter fandom. Maybe they found other fandoms or stories more appealing.
One possible reason could be that Naruto has seen the dark side of the shinobi world. He might have witnessed too much death and destruction in battles, and this has made him disillusioned. For example, if he lost many friends in a major war, he could start to question the whole concept of being a shinobi.