This is true and is one reason that free things these days are given "licenses" instead of simply being declared by their makers to be in the public domain. The public domain isn't what it used to be.
It's impossible to declare a work under the public domain in the USA. A creative work reaches the public domain only when its copyright expires, or if it's a government work.
Read up on the rationale behind the CC0 license for more information:
Read up on the rationale behind the CC0 license for more information:
https://creativecommons.org/about/cc0