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.
It might be for creative exploration. Writers often like to play with established characters and relationships. By making Naruto not care about Team 7, they can explore new story directions and character interactions that wouldn't be possible in the canon story.
One reason could be the author wants to create a unique and edgy story. By making Harry Potter not care about anyone, it's a complete subversion of the well - loved character. It grabs readers' attention.
One reason could be to explore Naruto's character independently. Without the focus on his relationship with Sasuke, the writer can delve deeper into other aspects of Naruto's personality, like his dreams for the village, his relationships with other characters like Kakashi or Iruka. It's a way to break free from the over - emphasized bond in the original story.
It could be that she has some past trauma related to Naruto's birth or the events surrounding it. For example, if she had a difficult pregnancy or if there were some threats to Naruto's life right from the start that made her distance herself out of fear. Another possibility is that she is under some sort of mind control which makes her act as if she doesn't care.
One possible reason could be a misdirection in his goals. If in the fanfiction he is overly focused on proving himself to the village, he might think that family is a distraction. So, he starts to distance himself from his family to concentrate more on getting recognition from the village.
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.
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.
Naruto could become more self - centered. Since he no longer has the overarching goal of protecting Konoha, he might focus more on his own needs and desires. For example, he could pursue personal power or adventure without considering the implications for the village.
It could also be due to some sort of mind - control or curse. In the Naruto universe, there are many powerful jutsus and dark magics. Perhaps an enemy has cast a spell on him that makes him not care about his own life. This would be a dangerous situation as he could be easily manipulated into dangerous situations without self - preservation.
Maybe the writer wants to explore a darker or more alternative version of Naruto. It could be a way to break the traditional view of his character and see how the story would unfold if he was cold - hearted.