TL;DR: A possible solution to the Fermi paradox is that a global society either collapses due to running out of resources before it expands into the galaxy, or survives by not expanding anymore, thus keeping it from expanding into the galaxy.

>survives by not expanding anymore, thus keeping it from expanding into the galaxy

The https://en.wikipedia.org/wiki/Aestivation_hypothesis could be a special case of this one. :)