Comment by teraflop

If you read the discussion, they weren't kept because of their encyclopedic value, or because they were "widespread". I'm not sure why the parent commenter said that.

They were kept to preserve a record of their having been uploaded, and to not create a legal risk for third parties who might be relying on the Commons page as their way to provide attribution.

The original proposal was to keep the image pages with the metadata, but delete the image files. That turned out to have some technical hurdles, so instead the images were overwritten with versions containing big ugly attribution messages, to discourage their use.