As for actual contact... many earth civilizations would rise and fall before a spaceship going at even 2% of the speed of light could reach such a planet.
As for actual contact... many earth civilizations would rise and fall before a spaceship going at even 2% of the speed of light could reach such a planet.
Perhaps every habitable planet develops life but only our plant has developed intelligent life. Perhaps only our planet among all the planet in the universe has life. Perhaps every planet develops civilization life and all such civilizations destroy themselves within about 10,000 years, leaving only hunter-killer robots.
In any case, interstellar space is so vast we couldn't practically other civilizations even if they turned out to be quite common in other solar systems.
On Earth, high tech civilization appeared relatively shortly after humans evolved. Agriculture was independently invented half a dozen times in different places, and cities and civilization at least twice in the new and old world. We were also moving in the direction of science and technology even before we discovered coal power so the "other planets don't have fossil fuels" doesn't seem like a great candidate either.
Edit: I agree we do know that human brings on earth are likely to invent agriculture.
But I show add there is even a view with no "Great Filter" at all. That is the claim that life on the Earth has developed with a steady, linear increase in log-complexity whose zero-point is fairly close to the big-bang. And thus the human species developing now is developing about as early as it could have, as quickly as it could have and so there's no surprise that no civilizations earlier than us elsewhere exist even if we plausibly expect these civilization to be appearing now.
Punctured equilibrium is a good theory to explain particular species diversity and morphology. It may or may explain increases in complexity as such and there may or may not be a tendency for the various jumps to even each other out over time.
I'm arguing I know such a theory is true, just that things are so complex that no theory is definitive.