One reason could be envy. Maybe Naruto sees Hinata as having something he doesn't, like a more stable family situation, and he lashes out in jealousy. Another reason might be that he's just being a typical, rambunctious kid who doesn't realize the impact of his words or actions on Hinata.
Well, it's not super common but it does exist. In some fanfictions, the 'Naruto bullies Hinata' scenario is used as a starting point to show character growth. For example, Naruto might start off bullying Hinata out of immaturity or misunderstanding, and then as the story progresses, he realizes his mistake and tries to make amends. This can lead to a deeper connection between them in the end.
Naruto's character would be presented as empathetic. He would understand how Ino feels when being bullied because he has been through it himself. So, he would not only save her physically but also try to comfort her emotionally. His character would also be depicted as strategic. Instead of just charging in blindly, he might first assess the situation and then use the most appropriate ninja technique to deal with the bullies. This would show that Naruto has learned to use his head as well as his heart in difficult situations.
One common theme is rivalry. The bullying can be seen as an extreme form of their rivalry. Another theme could be redemption, where Sasuke realizes his wrongdoings and tries to make amends.
One popular fanfiction might be where Hinata's bullying of Naruto is a misunderstanding. Maybe she was trying to get his attention in a really wrong way because she actually had a crush on him. For example, she could be stealing his lunch as a way to start a conversation, but Naruto takes it as bullying.
Some bullies might mock BTS fanfic. They could make fun of the fans who write or read it, thinking it's just some silly obsession. They might not understand the creativity and passion that goes into creating these fanfics.
Some bullies might mock or make fun of spiderman fanfic. They could see it as something only 'nerds' are into and use it as another reason to pick on fans. For example, they might laugh at the outlandish plot ideas or the 'geeky' passion of the fans.
Sasuke would be furious. He already has a strong sense of justice and loyalty to Naruto. He'd likely immediately start looking for Naruto, using his Sharingan to track any possible leads. He might even go against the village rules if he thought the village was involved in Naruto's kidnapping.
Sakura might be really surprised at first. She could offer to help Naruto with his girl disguise, teaching him things like how to do his hair or choose the right clothes. She might also find it a bit funny but would be supportive in the end, seeing it as part of a mission. Sasuke, on the other hand, might be a bit more aloof. He would probably just raise an eyebrow at Naruto's new look but wouldn't make a big fuss about it as long as it was for a good reason.