Perhaps magic itself has an influence on him. The world of magic he lives in is full of rules and expectations. Wizards are often expected to be strong and in control of themselves. Harry, being in the spotlight as 'The Boy Who Lived', might feel pressured to hide his emotions so as not to appear weak. He has to constantly face the public eye and the scrutiny of the wizarding community, which could lead to him suppressing his true feelings.
One possible reason could be his past traumas. Maybe he has witnessed so much death and destruction in his life, like the loss of his parents at a young age, that it has numbed him to some emotions. He has been in life - threatening situations constantly, which might have made him suppress his feelings as a form of self - protection.
Perhaps he was cursed. In the wizarding world, there are many dark curses that could affect a person's mind, and one such curse could target his emotional understanding. Also, it could be due to his isolation. Harry has often been alone or felt alone, and this lack of regular social interaction with a diverse range of people could have made it difficult for him to develop a normal understanding of emotions.
One possible reason could be to explore a different side of the character. By taking away his emotions, the writer can show how much emotions actually contribute to his actions and relationships. It's like a 'what if' scenario.
One possible reason could be to protect himself from the pain and loss he has endured. After all he's been through, like the death of his parents, Sirius, and so many others, turning off his emotions might seem like a way to avoid further hurt.
It could also be related to his self - preservation in the wizarding society. In a world full of magic and danger, showing too much emotion might be seen as a weakness. Harry, being aware of this, decides to shut out his emotions to appear stronger. He has faced a lot of scrutiny and jealousy from some students and even some adults in the wizarding world. By suppressing his emotions, he hopes to be more respected and less of a target.
Romantically, it can be a huge obstacle. If Harry has feelings for someone, like Ginny, his inability to express emotions would make it hard for her to know where she stands. She might feel unloved or unwanted, even if Harry has strong feelings for her inside. This could lead to misunderstandings and potential break - ups.
One possible reason could be that the magic used against him is of a very dark and ancient nature that defies the normal healing spells. For example, if it's a curse created by a long - forgotten dark wizard with unique and unbreakable properties.
It might be that in that particular fanfiction, the author was exploring different themes such as sacrifice on a grander scale. Harry Potter sacrificing himself to save the entire wizarding world in a more permanent way than in the original story. For example, perhaps the threat in the fanfiction was so great that his death was seen as the only solution to end the chaos and darkness.
One possible reason could be to gain more power. Maybe he thought that emotions were holding him back from reaching his full potential as a ninja. He might have seen other powerful ninjas who seemed to be emotionless and thought that was the way to go.
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.
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.