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 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.
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 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 a major betrayal. Maybe Hermione made a decision that seriously endangered Harry's life or the lives of their friends, like revealing a crucial secret to the enemy. This would be a huge breach of trust and could lead to Harry not forgiving her.
One possible reason could be miscommunication. Maybe Ron said something that Harry misinterpreted, leading to the distrust. For example, if Ron made a joke about Harry's abilities in a time of stress, Harry might take it the wrong way.
It could also be that in the fanfiction, McGonagall has shown some form of bias. Maybe she seems to favor certain students or groups over others, and Harry, being the one who always stands up for fairness, starts to distrust her when he notices this behavior. He might feel that she is not as just as he once thought her to be.
It could also be due to a long - standing pattern of behavior. If Ron had been constantly critical or undermining of Harry in the fanfiction, Harry might reach a point where he just can't forgive. Say Ron always made fun of Harry's decisions in front of others, which gradually eroded Harry's trust and patience.
Some members of the family might get angry. They may feel that Harry is being ungrateful for all they've done for him. They could start to spread negative things about Harry within the family circle or even outside to their friends.
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 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.