I think this is drawing on the vibe from animation styles where the artist draws several of the same frame, and minor imperfections are seen across each. (Dr. Katz etc seem to similarly be trying to mimic this.) A good example: https://www.youtube.com/watch?v=53s5uln_bw4

The question though is why does this look so appealing? I guess it's probably because in general we see motion as a proxy for if something is alive, since things that are alive are never completely still.