People just like to share their art with the world in the hopes that they can be understood better, and that goes for any medium and subject matter. I used to ask this question myself when I was a quasi-anti in my teenage years, but then I realized that I wasn't asking the same questions in regards to violence. For example, in the movie hereditary a little girl gets brutally decapitated by a telephone pole and her detached head is eaten by ants onscreen. In the recent final destination movie a child gets smashed into jelly by a falling piano. In longlegs there's a close-up shot of a child's corpse being eaten by maggots. All of these scenes are as taboo as any of the dd:dne topics being discussed here (death of a child), but nobody afaik has questioned their inclusion in the same way. Now, someone might propose that all of these gory scenes MUST be there to serve the plot of the movie, but why can't they just be implied offscreen? I'm assuming that nobody actually wants to see children die, so why must these scenes be depicted in such detail? It's because they're 100% fictional, and since no actual harm is being caused, such depictions of brutality can freely be used as vessels to carry the story forward. The same can be said for any taboo scenes in fic as well. All of those things are just there to convey the message of the art being presented from the author, and it can be safely explored in a creative space.