Earlier quoted context omitted.
The problem is not everyone on the world stage is a rational game theory nerd that links to papers like we want them to be. Also 60 years of treating every other country as a box in a threat model to be manipulated against other boxes has been a completely unmitigated disaster, so maybe we should stop that.
For all the evidence we have, MAD has worked. Still here. Still no WWIII. At the beginning of the twentieth century it was looking like we'd have another world war every twenty years or so for the rest of time. As best we can tell, nukes actually did end large-scale war. I would call that at least a partially mitigated disaster.
In the days of WWII, an attacker could rightly feel confident that there could not be an immediate response that strikes anything of importance. The attacker might even believe that such a response could not be possible ever in the future. Poland could be invaded without any realistic worry that Berlin would be attacked that same day, and a bit of optimism turns that into Berlin being safe.