The subject has been brought up before. The problem is that many people, especially newcomers, don’t realize that everything they post goes in the site-wide feed. Others only have time to visit once in a while. Both are just trying to get all their work into their personal gallery.
Unfortunately, WordPress doesn’t have any way to limit how many paintings someone posts, which would be the best way to handle it, I think. It can be annoying but unless someone is doing it constantly, I prefer to just let it pass.