Here's a blatant falsehood for us all to contemplate: Bans always work.

The truth is, all kinds of things are banned by treaty, by national constitution, or by law. The corollary to that truth is that those banned things are done in secret all the time, and--sometimes--not in secret at all.

Here's a case in point--torture is banned:

https://en.wikipedia.org/wiki/United_Nations_Convention_against_Torture

Even Syria has signed and ratified the Convention, but Syria in known to torture people. So does China. As does the USA. And Russia. And...and...and...

The nuclear ban is a beautiful, romantic ideal that does little but ensure that nuclear weapons research will be carried out in secret.