[rakoo]

The thing is, there is no universal notion of public domain. For instance, you could say that a work in the public domain belongs to no-one and/or everyone... but in France (and, as I juste learned, in the rest of Europe as well [0]) there is this thing that says that the creator of a work will always have paternity on it, forever.

I think most people have the same notion though, but as you know law is not just about notions, it's about hardcoding what's ok and what's not. This is actually what the CC0 tries to "solve": if there is no notion of public domain in the country you live in, then you apply the terms of the license, which happen to be what "public domain" would be.

[0] https://en.wikipedia.org/wiki/Moral_rights#In_Europe