It seems that the ancient records that many say are proof of extra terrestrial intelligence in earths past always incorporate some spectacular event or mass sighting. When Alexander the Great and his armies witnessed "UFOs" they were flying low and frightening his men. The Indian Vimanas were war machines of immense power and destrucive capabilities etc, etc...
And it seems that now the ETI have become much more passive, and with the world being more poplated now than it ever has been why have they suddenly decided to call it quits or just hover out of view.
I think this proves in some ways that either (A)What the ancients saw could be explained in more "down to earth" terms, or (B)the aliens are tired and just want to anally probe people for a while.