Well, you could explain that it doesn't align with your current preferences or that you have other commitments that prevent you from engaging with it. Be polite but firm.
Maybe he has a very traditional view on literature. He might prefer to stick to the original works and not engage with the fan - created versions. Fanfiction often takes the original story in different directions which he may not like.
Maybe he has his own reasons. He might be tired of the responsibilities that come with being a hero. In the fanfic, perhaps he has seen the dark side of heroism, like the constant danger and the loss of personal freedom. He could also be a complex character who doesn't conform to the typical heroic image.
After a novel was adapted into a movie or TV series, it would often lose some of the characteristics and style of the original novel. At the same time, it would also have a certain impact on the theme and content of the novel. Therefore, many novelists would consider whether or not to reject the film adaptation.
If a novelist refuses to adapt to a film or television, it may have a certain impact on their own creative career. However, there are also many successful novelists who successfully refuse to adapt to a film or television and continue to maintain the unique style and theme of their novels.
If a novel is adapted into a movie or TV series, it may have a certain impact on the author's creative intent and style. Therefore, the author may carefully consider whether to accept the film adaptation and how to maintain the characteristics and style of the novel to the greatest extent.
One possible reason could be moral conflicts. For example, if the fight involves harming innocent civilians, some Avengers might refuse. Another reason could be internal disagreements within the team. Maybe they don't trust the motives behind the fight or the leadership in that particular fanfic scenario. Also, they could be exhausted from previous battles and simply not in the physical or mental state to engage in another fight.
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.