High energy photons being what they are, at some point only more mass will protect against it. The same reason 10 minutes of bleach exposire kills most bacteria

High energy photons being what they are, at some point only more mass will protect against it. The same reason 10 minutes of bleach exposire kills most bacteria/virii but humans just get superficial burns. i.e., it's easier for multicellular life to develop resistance to these kinds of things than unicellular life