One possible reason could be a misunderstanding. Maybe Sakura said something that Naruto misinterpreted as being hurtful or dismissive of his feelings. For example, if she made a comment about his abilities in a negative way during a crucial moment, it could lead to him distancing himself.
Another reason might be that Naruto realizes his feelings for Sakura are unrequited and it's too painful for him to be around her. He may decide that cutting off communication is the best way to deal with his heartache. He could be thinking that by not talking to her, he can move on and focus on other aspects of his life, like his ninja training or his relationships with other friends.
Sakura might be initially confused. She could be thinking about what she did wrong to make Naruto stop talking to her. Since they have been friends for a long time, this sudden change would be very puzzling for her.
One possible reason could be that Naruto has finally realized that Sakura's heart has always been with Sasuke. After years of chasing after her and getting constantly rejected or overlooked, he just gets tired and decides to move on. He might start to focus more on his own personal growth and the other relationships in his life that are more reciprocal.
One possible reason could be that Naruto finally realizes Sakura's true feelings for Sasuke are unwavering. He might come to understand that his constant pursuit is fruitless and decides to respect her feelings and stop asking her out.
One possible reason could be that Naruto's character development leads him to focus more on other aspects like his ninja duties or his bond with other friends. As he grows, his priorities shift.
Perhaps there was some sort of dark influence at play. In the world of Naruto, there are often dark forces and genjutsu (illusion techniques). It's possible that Naruto was under the influence of a genjutsu that made him see Sakura as a threat, so he punched her in self - defense without realizing it was an illusion.
One possible reason could be that Sakura realizes she has different goals or values that are not compatible with being around Naruto. Maybe she discovers a new path in life that doesn't involve him, such as focusing on her own medical ninja career without Naruto's chaotic lifestyle interfering.
It could be that Sakura betrays Naruto's trust. For example, if Naruto entrusts Sakura with a very important secret, like something related to his family or his new power he's developing, and Sakura reveals it to their enemies or uses it against Naruto in some way, that would be a huge blow to Naruto and could lead to him crying.
It could be that Naruto has outgrown his initial feelings. As he matures, he starts to view Sakura more as a friend. In the fanfic, his experiences in the ninja world might have changed his perspective on love. He might have seen so much pain and sacrifice that he no longer wants to hold on to a love that might be one - sided or not as fulfilling as he once thought. Also, Sakura's continued love for Sasuke in the fanfic could be a factor that makes Naruto step back.
One possible reason could be that Naruto notices Sakura has been struggling with her medical ninjutsu skills lately and he believes an evaluation will help her improve. For example, she might have made some mistakes during a recent mission where her medical skills were crucial.
Well, in the fanfiction context, Naruto may not love Sakura because he has unrequited feelings for someone else. Maybe he has a deep connection with another character that makes him view Sakura just as a teammate. Also, their personalities might not be as compatible in a romantic sense as one would initially think. Naruto is often impulsive and headstrong, while Sakura can be a bit more reserved in some ways, and this could lead to a lack of romantic attraction.