Would OP consider the idea credible that most people are generally unwilling to cause the destruction of the world?

I'm not sure how one could show evidence for that as an 'explanation'.

The question seems leading... so what sort of answer are you looking for, OP?

Well thinking both east and west was the doctrine of Mutually Assured Destruction would keep the genie in the bottle and it worked. Doctrine works well when everybody has lots of infrastructure to destroy and all parties have some degree of concern about staggering loss of life they would endure.