Yeah. I don't like it, but after reading Rare Earth I am afraid I find this the most plausible explanation.
--Boris
Think back a few hundred years. Most of the population thought the world was flat and were totally unaware of the people living in Hawaii, and this was on our own tiny planet.
So here we are looking into a universe that contains billions (ok I'm sounding like Sagan LOL!) of stars. Many of them may be a possible harbinger to life. This life will look NOTHING like us. Even here on this planet compare a jellyfish to a giraffe.
Also the distances are so great and to date we have no reason to disbelieve what the equations that General relativity are showing us, No other life forms may be able to effectively travel outside of their own solar system.