It was done with other types of WMD, so why not nukes? Such bans come with extensive monitoring programs.

Also, it's better to have couple countries hiding few nukes so that they are not found by inspectors than thousands of nukes on hair trigger as we have today. An accident in the first case may wipe out one city or one country. An accident in the latter case will wipe out humanity as a whole.

Also kudos to South Africa who have destroyed their nuke cache long time ago!