The simulation includes this assumption:

> Technology persists in a given settlement for 100 million years before dying out

Seems wildly speculative to me. Our own civilization has only been around for a tiny fraction of that time and future prospects are already looking pretty uncertain. And if we lived in a galaxy where civilizations had this kind of longevity, one would think we'd see some evidence of potential signals out there.

My own pessimistic take on the Fermi Paradox is that life and intelligence may not be very unique but there is no reason for them to be long-lived either. Most civilizations are probably just a "flash in the pan", existing too briefly and separated by too great a distance to ever come into contact with another one (or even learn of another's existence).