I see your numbers, but I still don't understand the reasoning. We know technological civilizations can exist, the only question is the timeline. We don't know

I see your numbers, but I still don't understand the reasoning. We know technological civilizations can exist, the only question is the timeline. We don't know that interstellar travel is feasible under any timeline at all. How can you rate the second one more likely? (And as far as detecting relict machines: our astronomy is really not that thorough. They wouldn't even have to be hiding. Have we conclusively analyzed every little point of light in the asteroid belt? No.)