[cpitman]

Surrendering work to the public domain is actually more complicated. It's easy to make the claim that a work is public domain, but the law may not allow you to actually relinquish all copyright claims. This also depends on which country you are in.

This is why the CC0 license exists, to attempt to provide a more legally sound equivalent to plain public domain (https://creativecommons.org/public-domain/cc0/).