Maybe some people want to create shock value. They believe that by writing about an abused Kuroko Tetsuya, they can attract more readers. However, this is unethical as it distorts the character's image. Also, it could be due to a lack of understanding of the positive themes in the original work, which leads them to create such inappropriate content.
It could be that a small number of writers have their own personal issues or biases that they project onto the character. They might not have a healthy view of the character and instead use him as a tool to express their own negative emotions or ideas. This is not acceptable as it can harm the overall perception of the character in the fan community and goes against the respect that should be given to the original creation.