Septentrion_P said:
I'm pretty sure these images would have been approved years ago. Before this was a visual novel site, it was an anime site. Sometime, shading would include more than two colors, and it was considered nice and not required.
Years ago:
  • There was less art on the site.
  • The computer aided drawing tools artists use today did not exist or were much more crude, as a result the general level of artwork today is more detailed with better shading and more accurate lighting effects.
  • Different contributors, whose uploads are automatically approved and generally not intensively reviewed by moderation.
  • There was a different moderation staff.
We only delete old images if they don't meet the quantitative guidelines - occasionally such an image is flagged or a mod stumbles across one, otherwise these old images are grandfathered. Images more than a month old are generally grandfathered.

If you think an image should be kept, the most persuasive argument is to point out the specific attributes of an image that make is worth keeping such as a interesting shading technique/perspective/lighting effect, specific/interesting content.... comparisons to older or other images generally don't carry much weight.