Some places, like Germany, don't recognize a public domain at all.
A recipe for a cake is written on a paper and left on a bulletin board in town. It has no name and no one witnessed it being posted.
Everyone sees it and now knows how to make this cake.
The author may or may not be dead for 70 years.
Is it illegal to even document this cake recipe? You couldn't legally recount it in a news article or history text book without being able say who the author was and prove that they either granted a copy right or are known to be dead for 70 years?
Or worse, you are not only incentivised but essentially obligated to claim the authorship yourself just so you have someone to assign it to?
The thing undeniably exists regardless that the legal structure provides no place for it.
It's patently ridiculous. (guilty, terrible pun intended).
And there we come to the nuance of copyrights, at least in the US: you can't copy the text of the recipe, but the recipe itself don't have protection itself. Specifically, the text of the recipe is literature (which is protected), the recipe itself are instructions (which is not protected). This is the whole justification into clean-room design and reverse-engineering in software.
Also psuedonymous or even anonymous publications do have copyright (insert a legalheap of asterisks here). This actually sadly results into something called "orphan works", where they don't knew (or if they knew cannot find the next-of-kin/successor company/maybe even the government where the company was incorporated) where they can ask for permission.
(You can argue that there’s some legal risk at hand here; for example, if someone writes a book with the above and you start selling copies of it claiming you wrote it, the author can still come back and demand that you credit them as author and have that right enforced in court)
I think this is great. Case in point: blanket EULA for an image sharing site can not remove your right to be attributed, should your photo end up in an ad campaign or a newspaper. This means that many European newspapers actually make sure to not misattribute photographs, which has the side-effect of improving transparency in news reporting. So grabbing a photo online and wrongfully claiming it’s from the wrong time, place and source is not something that tends to happen in practice. And if it does, there’s a clear path to recourse that doesn’t require "lawyering up", you just file a claim with evidence.