In the simulations the authors are using, civilizations have lifetimes, meaning that all of them end after a while. And that simply isn't supported by events. Technological civilization has never vanished even from our little one-planet civilization. Polities do decline, but there is usually someone there to pick up the pieces. In an interstellar civilization there would be more recovery opportunities: interstellar visitors who arrive to see why a collapsed planet went offline.
The authors of this piece are asking us not just to assume that simultaneous disaster is possible on ten, a hundred, or a thousand planets. They are asking us to assume that it happens to every single time a civilization has achieved interstellar travel, and that it has been happening for the last ten billion years.
Simultaneous catastrophes on thousands of worlds affecting millions of species for billions of years? Life arising only once could easily be the more plausible option.