It might be due to a fundamental difference in values. If Harry has values that are completely at odds with his family's, like they are very traditional and he is very progressive, he could end up not caring about them. He may feel that he has no connection or common ground with them anymore.
One possible reason could be a long - held grudge. Maybe there were past incidents in the family that made Harry feel betrayed or neglected. For example, if his family always favored another sibling over him, it could lead to his apathy.
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.
It could be that Harry has a different view of family due to his unique experiences. He has been in a magical world full of danger and mystery, and his family might not be able to relate to that. He might feel that they are from two different worlds now, and his family's lack of understanding of his magical life makes him not care about them as much as he should in a traditional sense.
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.
One possible reason could be that he feels abandoned. His parents died when he was a baby and he grew up without them. He might think that if they were more careful or made different choices, they could have been there for him. For example, if they hadn't gotten involved in the fight against Voldemort in a certain way, they might have survived. Another reason could be that he has heard so many stories about them but has no real memories of them. It's hard to forgive someone you don't really know but are supposed to have a deep connection with just based on what others say.
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 possible reason could be that Naruto is so used to being on his own and having his own independent life. He has grown up without a traditional family for a long time, and the idea of suddenly having a family might seem very foreign and restrictive to him. He might fear losing his freedom and the self - made identity he has created over the years.
One possible reason could be a misunderstanding. Maybe there was some miscommunication in the past that led Naruto to believe his family didn't understand him. For example, if his family had different expectations for his future as a ninja compared to his own dreams.
In some fanfictions, Harry might leave his family because of a prophecy or a special mission. He might feel that he has to go it alone in order to fulfill this prophecy or complete the mission successfully. His family might not understand or be able to support him in this, so he decides to leave. Also, there could be jealousy or resentment within the family that makes the environment unbearable for Harry.
One possible reason could be that in the fanfiction, his family might have been portrayed as overly strict or controlling. Maybe they forced him into a certain path he didn't want to take, like a particular ninja training regime that Naruto found too rigid.
One possible reason could be a different upbringing in the fanfiction's alternate universe. Maybe he was raised in isolation or by people who influenced him to suppress family feelings. For example, if he was raised by a group that emphasized self - reliance above all else, he might grow up thinking family bonds are a weakness.