Some people write 'kakashi sakura hate fanfic' because they simply don't like the character dynamic between them in the original work. Maybe they think Sakura is too whiny or that Kakashi is too aloof towards her, and they want to explore a more negative version of their relationship.
There could be several reasons. One might be a lack of understanding of the characters' growth and development in the original story. If someone misinterprets certain actions or words of Kakashi and Sakura, they could end up writing a hate fanfic. Also, in some cases, it could be a form of expressing their frustration with the overall direction of the story. If they feel that the relationship between Kakashi and Sakura was not developed in a way they liked, they might create a negative version in their fanfic.
There are probably many 'kakashi sakura hate fanfic' out there, but I haven't really delved into them much. Some might be based on shipping wars, where fans of other pairings write negative things about Sakura in relation to Kakashi. They might write scenarios where Kakashi dislikes Sakura because she gets in the way of his relationship with another character in the fic, which is really just a way for the writer to push their preferred ship.
Another reason could be that some fans are purists. They only want to experience Pokemon through the official games, anime, and merchandise. Fanfic, in their eyes, is like an unauthorised and perhaps 'impure' form of Pokemon media. They might see it as something that dilutes the essence of what Pokemon is supposed to be.
People like it because it offers a different take on the Naruto universe. Kakashi and Sakura have a unique dynamic in the original series, and fanfiction allows for exploring a romantic relationship that wasn't fully developed in the anime or manga.
People write 'sakura likes naruto' fanfic because they love the characters. They see the potential in Sakura and Naruto's relationship. It's a way to explore the what - ifs. For example, what if Sakura had been more open about her feelings earlier? Also, it gives fans a chance to add their own creativity to the Naruto universe.
Some might hate Harry Styles fanfic because they feel it distorts the real image of the artist. They prefer to see him as he is in his official works, not in fictional interpretations created by fans.
Maybe he thinks fanfic often distorts the real story or characters of Naruto. In the original Naruto series, Kakashi has his own understanding and relationship with Naruto. Fanfic might create some scenarios that go against his view of Naruto or the world they live in.
Some people might write 'love you' fanfic because they enjoy exploring romantic relationships in the context of their favorite fictional universes. But if you hate it, it could be that you find it too cheesy or unrealistic. Everyone has different tastes.
Some people might write them out of jealousy. For example, if they prefer other characters and feel that Naruto, Hinata, or Sakura get too much attention in the original series, they might write bashing fanfics. It's a rather immature way to deal with their feelings though.
Some people write 'naruhina sasuke and sakura bashing fanfic' because they are die - hard fans of the Naruhina pairing. They might feel that Sasuke and Sakura somehow get in the way of the Naruhina relationship in the original story, so they create fanfics to emphasize Naruhina more by bashing the other two characters.
People could write 'naruto kakashi bashing fanfiction' for a variety of reasons. One reason might be that they have a different view of his actions and decisions in the original story. For instance, they might not agree with how he handled Sasuke's situation. Another reason could be that they simply want to create a more challenging or controversial narrative by making a popular character like Kakashi the target. It gives them a chance to explore different character dynamics and plot twists that deviate from the original story's glorification of Kakashi.