Because I introduced the topic of external sampling earlier in the thread (of ourselves by aliens, of lemmings by humans). In both cases these samples are necessarily randomized with respect to time, rather than lives. (Because we can't choose a life at random as observers outside the population unless we have a knowledge of the population profile against time, in which case we don't need Carter, because we have external information.)
Given that I'd inadvertently introduced a flawed example, I felt obliged to point out it was flawed and to explain the flaw. I can't get sniffy about other people's rotten explanatory analogies while allowing my own to persist!

Grant Hutchison