>>11814084
The point of the 3D cel shading method is to imitate the type of shading you'd do in real life on cels, with one or two flat colors rather than soft gradient transitions, hence the name

In the world of painting it was standard to try to capture every nuance, shade, and highlight on canvas using paints, but for visual mediums with a high required workload and output like comics or animation, flat coloring techniques had to be used to save on time and money and even to work around material limitations, cel shading in 3D exists to imitate these sort of flat shading / hard transition styles associated with cartoons/anime/comics in 3D where soft shading is effortless

You can technically animate with soft shading like Loving Vincent or Aleksandr Petrov's work but it's ridiculously time consuming so Loving Vincent animated by rotoscoping live action footage on canvas or in Aleksandr's case by painting on glass

https://www.youtube.com/watch?v=xdWJOGfu2wM

If someone made a 3D shader that looks like this movie, they would probably call it "glass shading" or "painterly shading"