Naruto's character might develop in terms of his leadership skills. As a king, he has to make tough decisions, which is different from his impulsive days as a ninja. He becomes more calculating and wise. Sakura, as a queen, may become more diplomatic. For instance, she used to be more straightforward in her approach, but now she has to use her words carefully to maintain good relations with other kingdoms.
One reason could be to add drama. By having Naruto hurt Sakura, it creates conflict which is a key element in storytelling. It can make the plot more interesting and engaging as it forces other characters to react and deal with the situation.
Naruto starts off as a lonely and mischievous kid who is shunned by the village. But through his encounters and challenges, he grows into a strong and respected ninja. He learns about friendship, love, and sacrifice. For example, his battles against Pain and his journey to bring Sasuke back all contribute to his growth.
Sasuke might develop by becoming more open and expressive of his emotions towards Sakura. He could start to show his love and care more freely, which is a big change from his usually reserved self.
It could be due to a dark influence. Suppose she was under the influence of some dark magic or an evil force that made her lose her true self and turned her against Naruto. This could lead to her almost killing him in the fanfiction.
One reason is to add some drama. In the Naruto story, Sakura and Naruto have a long - standing relationship. A slap can create an instant moment of tension. It can also be a way to show Sakura's strong personality. She's not one to hold back her emotions, and a slap can be a very physical way of expressing her feelings, whether it's anger or frustration.
People like it because it shows a different side of Sakura's character. Usually, Naruto is seen as the protector, but in these fanfictions, Sakura gets to shine in that role.
There are a few reasons. One is that some fans are really passionate about Naruto and they feel that Sakura didn't treat him fairly early on. So they use fanfiction to express their dissatisfaction. Another reason could be that compared to other characters like Naruto and Sasuke, Sakura's power progression might seem less exciting to some. So they create fanfictions to emphasize this perceived shortcoming. Also, there could be a sense of competition among fans for their favorite characters, and Sakura might be the target for those who prefer other characters in the Naruto world.
Another reason could be that some fans are so strongly attached to Naruto that they view any character who they think treats Naruto poorly as a target for criticism in fanfiction. Sakura, at times, did seem to take Naruto for granted in the original story. So, these fans write fanfictions to express their dissatisfaction with her character. Also, it could be a creative outlet for those who want to explore a different dynamic between Naruto and Sakura, one where Naruto is more assertive against her perceived flaws.