It could also be related to a prophecy or some kind of pre - determined fate. There might be a greater power at work that wants Naruto to be emotionless for a certain purpose, like in order to make a difficult decision without being influenced by his usual compassion.
One possible reason could be that he has been through so much trauma that he has numbed himself. For example, all the losses he has endured during his battles and in his personal life might have made him build a wall around his emotions.
Maybe some kind of dark magic or jutsu has been cast on him. In the Naruto universe, there are many powerful and strange techniques. It could be that an enemy has used a jutsu to suppress his emotions so that he can't fight back effectively.
Perhaps in the fanfiction, Naruto has had some bad experiences with Sakura. Maybe she has let him down in crucial situations, like not believing in him when he needed it most. This could lead to his feelings of despise as he feels betrayed by her lack of faith.
One reason could be his status as a jinchuriki. People might be afraid of him because of the Nine - Tails inside him, so he feels unloved. Another reason is that he was an orphan, and without his parents around, he may have felt like he didn't have that family love that others had.
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.
In fanfiction, Naruto could feel sick due to overusing his chakra. He often pushes himself to the limit in battles and training, and this excessive chakra use might take a toll on his body, making him feel ill.
It could be due to miscommunication. In the fanfiction, perhaps there were misunderstandings within the family. For example, Naruto might have overheard something that made him think his family didn't have his best interests at heart, but in reality, it was all a big mix - up. So, he gradually lost trust in them.
It could also be due to Sasuke's secrecy. If Sasuke is constantly hiding things from Naruto, like his real intentions or new powers he's acquired, Naruto would naturally start to feel that he can't trust him. Trust is built on honesty and openness, and if Sasuke is being cagey, Naruto's trust in him will fade.
His parents' death also contributed to his loneliness. Growing up without them, he didn't have that family support and love that most kids had. He had to fend for himself and deal with his feelings of abandonment all alone. And in the fanfiction, perhaps his friends are too busy with their own missions or problems, leaving him feeling isolated.
One reason could be that Sakura is confused about her own feelings. Maybe she has feelings for someone else and doesn't know how to handle Naruto's obvious affection towards her, so she lashes out and ends up hurting him.
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.
Well, Naruto could hate Sakura and Sasuke because in the NaruHina fanfiction context, Sakura might represent the past and all the times Naruto felt rejected by her. She always had eyes for Sasuke. And Sasuke, his actions were often self - centered and caused Naruto a great deal of distress. Naruto, as he falls for Hinata, starts to realize that Hinata is always there for him. Unlike Sakura, who is always pining for Sasuke. So, Naruto's feelings towards Sakura and Sasuke change to dislike as his relationship with Hinata blossoms.