Of course Bernstein isn't about to file lawsuits against his users, given his motives, but (prior to the public domain dedication) he might have stood a chance in court if people were downloading and using his copyrighted software without a licence. Under modern copyright law, all rights are reserved 'by default' (at least in the US). I'm not sure if a case like that has ever ended up in court, but I can't imagine any corporate lawyer signing off on acquiring and using software in that fashion.

An absence of lawsuits is not the yardstick for success here anyway. It's possible the public domain dedication deterred adoption compared to using a permissive FOSS licence. Consider Google's caution about public domain software for instance [0]. It could also be possible for software to be adopted but, if tested in future, this could be found to be legally murky.

If your intention is to make the code available to all, to do with as they wish, there's no legitimate reason to release it to the public domain rather than just using a permissive licence. If anyone with a deep knowledge of copyright law disagrees on this point, I'd be interested if you could post a link.

I'm not clear if you're doubting the correctness of what I said in my previous comment. I'm not making this stuff up, I already gave sources. The Creative Commons CC0 licence was created purely to address the legal complexities of the public domain. [1][2] (For other reasons of legal nuance, Creative Commons licences should not be used for software works, [3] but the point stands.)

[0] https://opensource.google/documentation/reference/thirdparty...

[1] https://creativecommons.org/public-domain/

[2] https://creativecommons.org/2008/04/16/cc0-betadiscussion-dr...

[3] https://creativecommons.org/faq/#can-i-apply-a-creative-comm...