Perhaps Naruto has grown weary of the excessive focus on Sakura in fanfiction. He might feel that other aspects of his life and the world around him are being overlooked. His own growth, his relationships with other characters like Sasuke, or his dreams for the village are not given as much attention as they should be in these fan - created stories. So, he's had enough.
Well, one reason could be that Sakura is often written as being too pushy towards Naruto in fanfiction. He might get tired of her always trying to boss him around or control his actions.
One possible reason could be that she might have underestimated Naruto in the past. She often belittled his abilities and dreams, but as she grew and realized his true strength and determination, she felt the need to apologize for her previous behavior.
One reason could be that Naruto has always been more attracted to those who understand his outcast past better. Sakura doesn't really have that kind of connection with him as she comes from a more normal background. So there's a lack of that fundamental understanding between them which hinders any romantic feelings.
A reason could be that Sakura says something really hurtful to Naruto about his dreams or his abilities. Naruto, who has always been sensitive about those things deep down, might lose his temper and punch her.
One reason could be jealousy. Suppose Naruto had achieved something that Sakura deeply desired for herself or for someone she loved, and in a fit of envy, she took drastic action. But this would be a very out - of - character move for the Sakura we know from the original series.
Maybe Naruto is sick of Sakura in fanfiction because her character is often portrayed as too pushy or one - dimensional. In some fanfictions, Sakura might be overly obsessed with Sasuke and Naruto just gets tired of her constantly going on about it.
In some fanfictions, it could be due to unrequited love. If Naruto has deep feelings for Sakura but she continuously rejects him in a cruel or thoughtless way, Naruto might feel angry enough to seek revenge. For example, she could publicly humiliate him for his feelings, which would hurt Naruto deeply and lead to thoughts of revenge. Another reason could be a misunderstanding. Suppose Sakura is misjudged by Naruto as having done something terrible when in fact she was innocent. But Naruto, in his ignorance, decides to take revenge. This can create a lot of drama and conflict in the fanfiction.
One reason could be jealousy. If in the fanfic, Sakura gets closer to someone else Naruto cares about, like Sasuke in a different way than he expected, it might make him hate her. For example, if Sakura teams up with Sasuke against Naruto's wishes in the fan - created plot.
One reason could be miscommunication. Maybe Sakura said something that Naruto misinterpreted as an insult to his dreams or abilities. For example, if she made a comment about his progress as a ninja in a way that came off as dismissive.
One possible reason could be Sakura's constant pining for Sasuke. Naruto might feel frustrated that she's so focused on Sasuke when he's right there for her. In the Naruto universe, Naruto has always been a bit jealous of Sakura's love for Sasuke, and in fanfiction, this could be amplified to the point where he yells at her out of pent - up emotions.