It might be because of a new influence in their group. Suppose a new character enters their circle and starts subtly turning his friends against Harry by spreading false rumors or making Harry seem less appealing in some way.
Another possibility is that Harry has been so preoccupied with his own problems or goals lately that he has unknowingly been neglecting his friends. So, in a way, their ignoring him could be a form of retaliation or a sign that they feel left out.
One reason could be a misunderstanding. Maybe Harry said or did something that his friends misinterpreted. For example, if he was overheard making a comment that seemed critical of them but was actually taken out of context.
One possible reason could be jealousy. Maybe Naruto has been getting more attention from the village elders or teachers because of his potential. His friends, feeling left out or overshadowed, might start to ignore him out of envy.
He might initially be confused. Harry could keep trying to engage with his friends as usual, not really understanding why they are being cold towards him.
Maybe his friends betrayed his secrets. In many fanfictions, a friend might accidentally or deliberately let out something Harry had confided in them, like his fears about Voldemort or his feelings for a certain girl. This could shatter his trust.
One possible reason could be jealousy. Maybe Harry has achieved something great and his friends can't handle his success. For example, if he gets a very important role in a magical competition, his friends might feel overshadowed. Another reason could be a misunderstanding. Harry might be wrongly accused of something, like being in league with the dark side, and his friends, in their fear or haste, abandon him without giving him a chance to explain.
One reason could be a misunderstanding. Maybe there was a miscommunication between Harry and his friends, and he felt so hurt or angry that he decided to leave. For example, if his friends wrongly accused him of something he didn't do.
One possible reason could be that he has some unresolved issues from his past, like the absence of his parents during his childhood which made him feel a sense of detachment. Maybe he is so focused on achieving his ninja goals that he unconsciously starts to ignore his family. Another reason might be some sort of miscommunication within the family. For example, if there are secrets that the family has been keeping from him, he might feel betrayed and thus choose to ignore them.
One reason could be jealousy. Maybe Harry has achieved something great like getting a special magical power or a high honor in their magical world, and his friends feel envious. Another reason might be a misunderstanding. For example, Harry could have been wrongly accused of something, and his friends believe the false rumors without giving him a chance to explain.
Another reason might be jealousy. If Harry suddenly gains more power or attention in the fanfiction world, his friends could become jealous. For example, if he discovers a new and powerful magic spell, and all the focus in the magical community is on him, his friends might start to feel overshadowed and distance themselves from him.
One possible reason could be an alternate universe scenario. Maybe in that fanfic's universe, there are dark forces at play that make Lily and James act out of character and ignore Harry. It could also be a plot device to create a more angsty or dramatic story, where Harry has to face challenges without the support of his parents.
One possible reason could be that Naruto is afraid of endangering his friends. He has many powerful enemies, and he might think that by staying away from his friends, they won't be targeted. For example, Orochimaru was always after Sasuke, and Naruto might fear that his closeness to Sasuke could put Sasuke in more danger.