One possible explanation for the "no contact" situation isn't listed in the lead article: technological stagnation. An intelligent bunch of aliens could be frozen for millions of years in ancient-Egypt-like societies. Most human societies have been that way. Such societies can be very stable. It tales a wild technological leap to get to where we are. Perhaps that's what's really rare.
technological placemarker, because it's time to go watch the "Star Trek" babe with the "gravity-defying" breasts....
Indeed. This is just one more reason that the Fermi Paradox is flawed.