The problem is more that "public domain" is a concept that is not universally accepted in a legal sense, examples are Europe and in particular Germany. Case in point, Sqlite had to come up with a license agreement to make it usable for companies in those countries.
Public domain exists everywhere, but the concept of releasing something into the public domain by choice doesn't, so in those jurisdictions something only officially enters the public domain some time after either the author's death or publication.
The mental model of GPL cancer has infected the concept of public domain