[Islandman59]

I have a very basic theory:

Perhaps the genesis of life needed (or took) a certain amount of time to evolve or transpire, so that would explain why there may not be civilizations that are far more advanced than ours. Maybe we are slightly ahead of most. Maybe the building blocks of life have always existed throughout the universe in old galaxies and asteroids all along, and the final ingredient (time) needed to be added before it could begin the process. Then this “fertile” state was spread by asteroids to newer planets.

[G Anthony]

No mention of variations on the anthropic principle. Like, we ARE the extraterrestrials. Trivial, it's true. But, there is another thing, we have been seriously looking for only a few decades. Why is it surprising that we have not yet found what we are looking for? Give us another few hundred years and then come back to me and say there is a true paradox here.

[Widdekind]

Hypothesized "Dyson spheres", wrapping around then-hidden central stars, would plausibly re-radiate at ~300K. Such "stars in bags" would plausibly resemble ultra-cool, ultra-large red-giant stars, e.g. RGB, AGB.