Perhaps Naruto is in a state of deep depression. He has faced so many challenges and losses throughout his life that he has simply given up on talking to others. He may feel that no one truly understands him and that his words would be of no use, so he chooses silence as a form of protection.
It could be related to some kind of curse or jutsu gone wrong. There might be a hidden enemy who cast a spell on Naruto that restricts his ability to communicate. This would be a very interesting plot point as it would force Naruto to find a way to break the curse while also dealing with the isolation.
One possible reason could be a traumatic event. Maybe he witnessed something so horrible that it made him shut himself off from everyone. For example, if he saw his friends in great danger and couldn't save them in time, it might have led to his silence as a form of self - blame.
Perhaps he's under a powerful genjutsu. In the Naruto universe, genjutsu can manipulate a person's perception and behavior. It's possible that an enemy has cast a genjutsu on Naruto that makes him believe that if he talks to anyone, something bad will happen to them, so he chooses to remain silent.
Perhaps Naruto is focused on his own personal growth and training. He might see the yaoi relationships around him as a distraction from his goals of becoming a stronger ninja. He could be thinking that engaging with others involved in yaoi would lead him astray from his path of self - improvement.
One possible reason could be past betrayals. Maybe he has been let down by people he thought were friends in the fanfiction world. For example, if someone he trusted shared his secrets which led to him getting into trouble.
In some fanfictions, the author might make fem Naruto not talk to create an air of mystery around her character. By not speaking, she becomes more of an enigma, which can draw readers in. It could also be related to her character development. For example, she may be shy or introverted at the start of the story and gradually learn to open up and speak as she grows and overcomes her insecurities.
It might be due to hidden secrets. If there are dark secrets within Konoha that Naruto discovers in the fanfiction, such as a conspiracy that involves some of the higher - ups. This would make him lose trust in the village as a whole.
It could also be due to Sakura constantly doubting Naruto's abilities in the story. Naruto has always been looked down upon by many in the original series, and if in the fanfiction Sakura continuously expresses her lack of faith in him, it could lead to his unforgiveness. For example, she might have refused to believe in Naruto's new jutsu or his plans to save the village, which made Naruto feel really disappointed and unable to forgive her.
One possible reason could be that Naruto has had some past experiences within the team that made him feel betrayed or let down. Maybe there was a mission where he thought his teammates didn't have his back. Another reason might be that there are secrets among the team members that Naruto has discovered, and these secrets make him question their loyalty. For example, if one of his teammates was hiding a connection to an enemy, Naruto would naturally start to lose trust.
One possible reason could be that he feels betrayed by Konoha. Maybe he has uncovered some dark secrets about the village that make him lose faith in it.
Well, it could be that the fanfiction is set in a very different universe where Naruto has different upbringing or experiences. But this is quite a stretch because Naruto's caring side is so deeply rooted in his story. It might also be that the writer is simply trying to create shock value by presenting such a counter - intuitive view of Naruto. But in general, it's not in line with the essence of Naruto as we know him from the original series, and it might be a bit of a gimmick to make the fanfiction stand out in a sea of more traditional Naruto stories.
One impact is that it can change the dynamic between Naruto and other characters. Since he's not talking, other characters might have to take on more of a communicative role. For example, Sasuke might have to be more perceptive of Naruto's non - verbal cues, which could lead to a different kind of relationship development between them.