Another reason might be that Naruto has been influenced by external forces. Maybe he has made some bad friends or been involved in some situations that made him think being cold to his family was the right thing. He could have been brainwashed into believing that his family was holding him back from achieving something greater.
One possible reason could be that Naruto has his own unrequited love for someone else and he is trying to distance himself from Sakura to avoid leading her on. For example, if he has deep feelings for Hinata, he might be cold towards Sakura to make his own feelings clear.
One reason could be that Naruto is focused on his own goals like becoming Hokage and he might see Sakura's feelings or her actions as distractions. He has a lot on his plate and may not have the time or energy to deal with her in a warm way.
One reason could be that Naruto has been through so much himself and he might think rookies are naive. He's seen the harshness of the ninja world and doesn't want to coddle them. For example, he had to grow up without his parents and faced many life - threatening situations early on.
One possible reason could be a misunderstanding. Maybe there were some miscommunications in the family that made Harry feel alienated, so he became cold. For example, if his family misunderstood his intentions in certain matters, like his career choice or relationships, it could lead to this situation.
She might be confused at first. Sakura is used to Naruto being friendly and now his coldness would be a big change. She may start to question what she did wrong.
It can create a lot of tension. For instance, other family members might try to figure out what's wrong and this can lead to various sub - plots. They could try different ways to win Naruto back, which would add more drama to the story.
It may also lead to Naruto making different choices. Instead of relying on his family for support, he might turn to other sources. This could drive him closer to some characters he wouldn't have been close to otherwise, and change the power dynamics in the story. For instance, he could side with a group that his family is against, just to show his independence from them.
It could also be due to some external influence. Perhaps an enemy manipulated Naruto's mind in the fanfiction, making him see his family in a negative light. This enemy might have used some form of mind - control or false memories to turn Naruto against his family.
One possible reason could be that he has faced a lot of misunderstandings within the family. Maybe his family has certain expectations that he can't meet, and over time, this has led to his coldness. For example, if his family doesn't understand his dreams or ambitions, Naruto might feel alienated.
One possible reason could be a feeling of betrayal. Maybe he found out some long - hidden family secrets that made him lose trust in his family. For example, if he discovered that his parents had made a deal with some dark force in the past that had negative consequences for him or the village.