You do realize that the instant death part of a blast is only for those in the immediate detonation crater area, whereas dozens of miles of blast zone in all directions beyond that tend to feature some of the most extreme human suffering ever conceived by mankind, right?

People with half their skin melted off in disintegrated buildings over the next few miles, then blindness, flattened homes & guaranteed cancer for the next few miles, and then slow-kill radiation out for 10 miles beyond that... And then of course the hospitals are all flattened and there is no drinkable water for 100 miles in any direction... Fun times indeed!