Another possible explanation is advanced civilizations quickly move on to more advanced forms of communication. We're already on the cusp of quantum communication. Would we even still be using radio in 100 years? A couple hundred years of our civilization using radio technology would only be an extremely brief period of time on the cosmological scale. Maybe technologically advanced civilizations progress in rapid jumps like ours did with the industrial revolution, the age of electronics and now the digital/information age. We're looking for other civilizations at our current level of technology which may be a brief window of time overall for technologically advanced civilizations.<p>And if they are at our current level of technology they would be stuck on their planet like we are and have no viable way to reach us no more than we could reach them.<p>Or they could still be using radio but using fully encrypted communications. Weak signals reaching Earth from over vast distances would appear like and get lost in the background noise of cosmic radiation.
Having no better estimate, might as well use Earth.<p>What is the most prevalent/enduring symbiotic relationship?<p>[0] <a href="https://en.wikipedia.org/wiki/Symbiosis" rel="nofollow noreferrer">https://en.wikipedia.org/wiki/Symbiosis</a>