A closed species is a fictional species that is claimed to be owned by someone who limits the way in which new characters can be created. Most (if not all) closed species are claimed to be protected under copyright, but a species is too broad of an idea to be protected by copyright, and therefore they aren’t.
I think @alcoholicorn is saying because the art is so shitty, no one really wants to steal the apes for their own sake. This makes the bored ape “species” safer from “theft” than if they had actually made a well executed art piece and made efforts to stop people from “stealing” / using it.