Another reason could be related to his relationships. Maybe in a fanfic, Naruto has a falling out with his friends like Sasuke or Sakura. This emotional hurt can be just as painful as physical harm. The author might use this to show how Naruto grows and overcomes such internal struggles.
One reason could be for the sake of creating unique power dynamics. If Naruto is an Uchiha, he could potentially have access to the Sharingan or other Uchiha abilities, which would make his battles and character development very different.
One reason could be some sort of special jutsu or power - up. Maybe he got a new form or ability that suppresses pain. For example, it could be related to his Sage Mode or something new entirely.
These fanfics can also inspire fan art and discussions within the fandom. Fans might draw Naruto in his hurt state, or have in - depth discussions about how the events in the fanfic could have been different. This helps to keep the Naruto fandom active and engaged, even if not everyone agrees with the concept of Naruto being hurt in fanfics.
One possible reason could be that Naruto is so focused on his goal of becoming Hokage. His mind is occupied with training and achieving power, so he seems cold to Sakura. He might not have the time or mental space to show her more warmth.
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.
It could also be due to jealousy. If Naruto is spending a lot of time with other female characters, Hinata might get angry. Even though she is usually shy and reserved, her love for Naruto could turn into anger if she feels threatened by his closeness to others.
One reason could be that Naruto has grown weary of Sakura's unrequited love for Sasuke. He might feel like she's always focused on Sasuke and doesn't truly see him, Naruto. Another aspect could be that Sakura's constant nagging or her over - emotional outbursts have started to grate on Naruto over time. Maybe he's also tired of having to be the one to always cheer her up when Sasuke - related things go wrong.
Maybe he was blamed for some trouble he didn't actually cause. For example, if something went missing in the orphanage and the caretakers wrongly thought Naruto took it.
One possible reason could be some kind of dark magic or jutsu that has affected his family's memories. Maybe an enemy cast a spell specifically to make his family forget about him to weaken him.
One popular 'Naruto is Pain' fanfiction could be 'The Transformation of Naruto into Pain'. It might explore how Naruto, through some unique circumstances, begins to adopt Pain's ideology or power. Another could be 'Naruto: Pain's Legacy' where Naruto has to deal with the after - effects of Pain's actions in a very personal way.