Just how would you go about banning nukes and making 101% sure everyone who had them complied and stop new people from developing them.
This issue has been discussed and researched for a long time. There are existent plans for inspection and detection that are highly developed. Some of them are similar to those used for the Iran agreement - which worked well until the US bailed on it. And there is a network of seismic detectors in place and operational . .
And there might well be nations that refuse to make nukes, but then change their minds - like North Korea. For that you want to look into the literature on "Break-Out".
There are also huge environmental. social, political, and economic costs of having nukes.
Aotearoa made the right choice.