One possible reason could be his past traumas. Naruto grew up alone and was often shunned by the villagers. Physical touch might remind him of the times when he was pushed away or bullied, so he has developed an aversion to it in fanfiction.
It could also be related to his ninja training. He is always on guard and being touched might disrupt his focus or make him feel vulnerable in a dangerous ninja world. He has to be constantly aware of his surroundings, and unexpected touch could be seen as a threat to his safety.
Well, in some fanfictions, it might be because the writer wants to create an alternative storyline. Maybe they think Naruto has a different type of relationship in mind, like a more platonic or brother - sister - like bond with Hinata instead of a romantic one.
Maybe in some fanfictions, the writer portrays Kakashi in a way that Naruto doesn't resonate with. For example, if Kakashi is written to be too strict or distant in a different way than in the original story, Naruto might not like that version of him.
One aspect could be that it might explore a Naruto who is in a state of being 'untouchable' in a metaphorical sense. Maybe he has some sort of power or status that makes him unapproachable. For example, it could be a story where he is so powerful that other characters are in awe and can't physically or emotionally reach him.
Obviously Naruto himself. Then there could be his friends like Sasuke and Sakura. Since Naruto is in this 'untouchable' state, they might be the ones trying to figure out what's going on and how to reach him again. They have a deep connection with Naruto, so they would be likely characters in the story.
Well, some fans might create such fanfiction because they think Naruto's relationship with Sakura was more of a friendship. They feel that Naruto had a deeper bond with other characters like Sasuke in a different way than a romantic love for Sakura.
Maybe it's a powerful jutsu or curse that doesn't eliminate the characters outright but instead forces them to find a way to adapt and survive, leading to interesting plot twists.
Maybe it's related to his sense of independence. Naruto is used to relying on himself and having others touch him might make him feel like his personal space and autonomy are being invaded. He's always been on a journey to prove himself, and being touched could be seen as a form of interference in that self - discovery process.
Maybe Peter doesn't like the way Steve is portrayed in fanfiction. Some fanfictions might deviate too much from the original character, and Peter prefers the official version of Steve.