It's not entirely arbitrary - the fact that the US is not a small island about 1000 miles from its nearest neighbour seems to comprehensively eliminate the New Zealand-style elimination option, given the trouble they're having with it. Like, even if you assume an equally competent lockdown in the US would have the exact same per-capita chances of infections slipping through from outside, with no disadvantage from the porous southern land border with a country that has a major outbreak, it still has 100 times the population. Which means that rather than causing a new major imported cluster once in 100 days, the leaks which the New Zealand government can't identify, fix, and reckons are likely an inherent limitation that they'll just have do deal with would cause them roughly daily. That means no elimination, not even if the numbers worked out slightly better than my rough estimate. And remember, New Zealand was the last big, well-known elimination success story left standing.