One possible reason could be that Naruto has grown tired of Sakura's violent tendencies towards him. He might have reached a point where he decides to stand up for himself and not tolerate being hit any longer.
She might be shocked at first. Sakura is used to Naruto being more passive when it comes to her hitting him, so when he suddenly stops her, it could catch her off - guard.
There could be prejudice against certain magical creatures. Maybe there are some creatures that are considered dangerous or inferior in the wizarding world. But Harry, in this fanfiction, doesn't go along with that. He takes the time to understand the creatures, like he did with Buckbeak. He doesn't let the general prejudice towards these creatures make him treat them unfairly.
It's also possible that he is a mysterious character who has some sort of connection to Sakura's past or her powers. His presence might trigger something in Sakura, and she can't let him go until she figures out that connection.
One possible reason could be that he has some crucial information that Sakura needs. Maybe he knows secrets about their world or a powerful enemy, and if he escapes, that knowledge will be lost.
Maybe Naruto just sees Sakura as a friend. He might have a different idea of his ideal partner and Sakura doesn't fit that. His feelings for her could be purely platonic.
Well, some fans might create such fanfiction because they think Naruto's relationship with Sakura was more of a friendship. They feel that Naruto had a deeper bond with other characters like Sasuke in a different way than a romantic love for Sakura.
In the fanfic, it could be that Sakura has her own reasons for not speaking to Sasuke. She might be trying to protect him in a strange way. She could think that by not speaking to him, she can keep him at a distance from some danger that she anticipates. It's a rather self - sacrificing act on her part.
In the fanfic, Sakura might not speak to Sasuke because of a past misunderstanding. Maybe Sasuke did something that Sakura misinterpreted, and she's so hurt that she refuses to talk to him.
One possible reason could be a clash of personalities. For example, if Naruto is too impulsive and his team members are more cautious, it can lead to friction. Maybe in the fanfic, Naruto's unwavering belief in his own way of doing things doesn't align with the more strategic or traditional approaches of his teammates. This could cause misunderstandings and make it seem like they don't work well together.