[wongarsu]

Germany would be one example. Public Domain exists, but only as the state something enters after copyright expired naturally 70 years after the death of the author. You can't release things into public domain.

As for why: nobody considered that case when writing our copyright laws, and nobody bothered to change it. Copyright as designed can't be transferred (except through inheritance), to avoid exploitation of the original creator. As a consequence you can't really get rid of it, you can only grant licenses.

It's hardly the only right you can't get rid of, and CC0 tries to deal with some of them, like the right to one's one image which in the shortest possible form says that you can't create or publish a picture of a person without their consent (but as you can imagine is way more complicated than that). You could say that the German legal framework isn't about maximizing freedom, it's about maximizing happiness, and sometimes being able to give away a right or freedom will on balance cause more harm than good.