So... a civilization ( or, a few civilizations ? ) so far advanced to be able to travel interstellar distances, continues to play "peek-a-boo" for so many years ?
I'm not being silly here. This logic isn't the best, but makes a point.
1. We believe life requires water & we're finding water just about everywhere we look, so that's not an issue.
2. There are more known stars (we can't see all of them, even in our own universe) than there are GRAINS OF SAND ON EVERY BEACH IN THE WORLD and almost all stars have at least a few planets around them. Think about how many grains of sand are on ONE beach.....that's freaking incredible.
3. It's just the odds are pretty dang good......if there's life on only 1 out of 1,000,000 planets, even little bacteria, then there are LITERALLY millions of planet/moons with life on them. They're just too far away for US to see/know about them with our basically "cave man" telescopes & "cave man" space ships. We'd DEFINITELY need some type of "warp drive" to ever visit even 1% of the planets in our universe.
4. Here's the "stretch of imagination" --> We live on an average size/age planet orbiting around an average size/age star (the Sun), so I'd "guess" we're about an "average" civilization. Half of life out there is probably less advanced (think bacteria or whatever) and half of life is probably more advanced than us. Only the few very, very advanced "people-type life" could travel around the universe or even send us a signal....VERY few.
5. We'd have to be WAY more advanced to find other life (except "maybe" some bacteria or something in our own solar system), so it's probably only a very small fraction of life out there that actually has a "warp drive" and can come visit us.
6. I honestly believe that we're like "monkeys in a zoo" in the sense that some of these VERY FEW super-advanced races that have a "warp drive" would be curious just to take a look at us...probably not wanting to "invade" or anything....just curious to look at the simple little humans, just like we like to look at the simple little monkeys in the zoo.
If we find even a trace of life not on Earth....would you be convinced then?