As an unspoken rule, people are not allowed to say anything negative about an image. And in the rare instances that they do, they are quickly labeled "trolls" and the artist winds up crying that someone posted a negative comment on their image. "What do you mean the shadows aren't right? I can't stand this place any more. I quit!" As a result, many comments have been reduced to the generic "nice" or "how cute" or "that's adorable". Those may be good ways of saying you like the image, but it doesn't exactly help the artist to hone their skills.