I cannot speak for the people responsible for drafting those treaties, but it appears to have been a timely effort to apply multi-lateral pressure against proliferation. Put another way: for some nations to pull up the ladder. Not long-term thinking perhaps, but medium term at least.

In the longer term, who could have known then or even cared how to maintain the transition to a no-test regime? What the treaties' drafters might have been thinking is now moot. Those people are long gone, it's your problem now.