Why theano UFOs

OK, first off, yes, there ARE UFO's. There may not be alien
spaceships, but UFO simply means Unidentified Flying Object, and so
any time somebody sees something in the sky and doesn't know what it
is, that's a UFO. Whether it's swamp gas, an experimental military
aircraft, or the Eridanian mothership is another question.

OK, now that I've got that off my chest...
I've wondered if maybe the aliens are all on their home planets,
wishing they'd built powersats before their oil and coal ran out.
Maybe they didn't have a big, nearby moon to pull them into developing
their capabilities early. Or maybe they did, but didn't have a Cold
War to speed technological development.

Or maybe no civilization manages to save itself, and neither will we.