This actually was kind of the nugget for me in this story: "At one extreme, it is easy to make the galaxy empty by simply shrinking the number of usable planets

This actually was kind of the nugget for me in this story: "At one extreme, it is easy to make the galaxy empty by simply shrinking the number of usable planets and having civilizations last for only, say, 100,000 years or so." i.e. 10x longer than we have had even rudimentary technological civilization on our own planet. Sample size of 1, etc. but this to me seems the simple explanation of the "paradox". Space is big, and 100k years is a long period of time to not make a mistake.