Maybe he just didn't care much about fan - made stories. He was so used to his own real - life adventures in the wizarding world that fanfiction seemed unimportant to him.
Well, in the wizarding world, he was focused on more important things like fighting dark wizards, protecting his friends and family, and dealing with the politics of the magical community. Fanfic was just something that happened outside of his main concerns. It was like a side - show that he didn't have the time or inclination to pay attention to. He had enough on his plate without getting involved in the fictional creations of his fans.
One possible reason could be that fanfiction often takes the original story in directions that might not align with the author's vision. J.K. Rowling, who created Harry Potter, had a very specific world and story in mind. Fanfiction can sometimes distort or change elements of that world in ways she might not have intended. Also, from a legal and copyright perspective, it's a bit of a gray area, and she may have wanted to distance herself from it to avoid any potential legal issues or confusion about what is 'official' and what isn't.
Naruto could ignore fanfiction because it often contains elements that are not part of his reality. The fan - made stories might distort his character or the relationships he has. For example, some fanfiction might pair him with characters in a way that doesn't make sense to him or goes against his values, so he just ignores it.
It could also be for the sake of creating a different plotline. Writers might want to explore how Harry would develop without the support of his father figure. So they make James ignore Harry to see how Harry overcomes the challenges on his own.
Maybe he's too busy with his own adventures in the original story world. He has quests to go on, friends to save, and monsters to fight. Fanfiction might seem like a distraction from his real 'job' in the Percy Jackson universe.