If there is another civilization, it is entirely possible they didn't need saving, unlike our sinful selves. It is possible we have no contact with other civilizations because we alone out of all the teeming universe are considered "bad seed" and exist only by the Grace of God. Those other people are still living in their Gardens.
What if its not just one other civilizations, but thousand or millions and we are the only "bad seed". Talk about feeling left out!