So, assume 10 of them do make it through defenses. One hits Boston, NYC, Philadelphia, DC, Norfolk, Miami, Chicago, San Diego, LA, SF. That's 28 million people and most of the political, financial, administrative, logistical, shipping and naval centers.

Sure, humanity survives. But in a state akin to Europe in 1918. Massive casualties, destruction, horror, economic calamity, famine, general chaos, which will persist for at least a decade. And this would be in every major developed nation. So... perhaps it is not a good idea to use them. Perhaps the "misconception" that the world will end is the only reason they haven't been used.