I think there may have been a lot of intelligent civilizations in the universe, maybe in the millions. But the question is do they exist close enough in both time and space to discover each other? If an advanced civilization had come looking for intelligence on Earth as little as 10K years ago, it would have found none (except for some cave dwellers making paintings and using hunting tools). And 10K years is nothing in the life of the universe.
Based on the dynamics I see here on Earth, I think it is likely that a species will reach technological greatness and then devolve back into sub-intelligence. This could be caused by war. It could be as simple as losing the moral framework that made their intellect possible. In all things with a biological basis, I think the genes contain both the seeds of potential greatness and self-destruction.
“If an advanced civilization had come looking for intelligence on Earth as little as 10K years ago ...”
Yes, But had they come 2-3 thousand years earlier, they may have found an advanced stone based civilization - remnants of which are being discovered currently - we still have no idea what the pyramid complex at Giza was built for and what its purpose was; see Gobeki Tepi, buried deliberately 12,000 years ago - why and who are unknown; see evidence of a double comet strike - one ending the Ice age and another 1,000 years later causing the Younger Dryas. (This heralds another possible strike from the same Taurids group in the next 50 years as we pass through a denser portion of the group.)
Meanwhile, any evidences of civilizations before that time would be so degraded as to be unrecognizable or nearly so today.
“And 10K years is nothing in the life of the universe.”
And 10K years is nothing in the life of the Earth. And 10K years is nothing in the history of homo sapiens ... going back at least 250,000 years (according to mitochondrial DNA findings).