If people make something that is actually copyrightable, and they restrict access to that, then sure. It's their right as the copyright owners to restrict adaptation of their content.
However, whether or not a "cat-fox" is copyrightable content is questionable, and very unlikely in my unprofessional opinion.
But something like this
could be copyrighted, I think. She made a whole species dubbed "Dewsquilli" and I can't see any direct resemblance to any existing creature (other than the obvious building blocks: bones, flesh, torso-limbs-head type stuff), so I'd say that qualifies as an original work that she now owns.
Sure, anyone sneaking a copy of some girl's creature design probably wouldn't be given much attention by authorities, but that doesn't mean it's not wrong to take from her what she wants to keep for herself. It's her right as the original creator and that right should be respected. In a perfect world...
also the fact that not a lot of "original species" out there are nearly as distinct as this one, and thus people will either not care about them or fight over how similar someone else's "species" looks to their "species" and who came up with it first, which is just silly, pointless and mind-numbingly tedious to watch unfold (which is why I don't delve into any of that~).