Radiance and the Lingering

On a brilliant fall afternoon, a powerful blast of energy erupted from the cosmos, burned across the solar system, and laid waste to every living thing on Earth. Notice was short and defense impossible. From the lowliest to the loftiest, none survived. This phenomenon, they called the Radiance. Curiously, however, none died, either. Instead, thereafter the hapless victims of that unavoidable catastrophe wandered the planet in a discorporate, ethereal state of existence. This, they called The Lingering. In time, as the effects of the apocalyptic radiation dissipated through the course of untold centuries, a mysterious collection of bizarre artifacts would reveal the truth behind their curious circumstance.

When a powerful, unavoidable cosmic apocalypse irradiated the entire planet, every living creature succumbed. Yet, all were spared a natural death. Why?