Although that’s one of the many possible explanations of the Fermi paradox [0], I prefer to think that the real reason we haven’t discovered (or we haven’t been discovered) is the fact that we’re limited by the speed of light.
The distances are so vast, almost unfathomable, that we need Faster Than Light means of traveling. Perhaps I’m being naive or romantic, but I prefer to think this is the real reason :-)
Also as particles spread out, there's less of a chance of interaction, which by extension makes it so there's less of a chance that a system of electrical impulse that fires in a synapse would exist over large distances. This system, of course, would be the catalyst for producing such thoughts as "I wonder if we're alone in the universe."
That's not to say you can't send dense information over larger distances with a shorter wavelength (re: radiation; gamma rays)... it just means the flying saucers with little green men landing on earth are probably out.
The speed of light and great distances are indeed a limiter, but the universe has been around for billions of years. Even with the great distances, an interstellar civilization that's been around for millions of years would have had plenty of time to find us by now.
The distances are so vast, almost unfathomable, that we need Faster Than Light means of traveling. Perhaps I’m being naive or romantic, but I prefer to think this is the real reason :-)
[0] https://en.wikipedia.org/wiki/Fermi_paradox