The implicit assumption is that not only does a technologically advanced society exist, but they also have the ability and desire to create space-faring self-replicating robots. So, on top of the other restrictions involved with the Fermi paradox, you're adding: Being on a planet where the gravity isn't too strong for space launches using available materials. A society that wants to spread out into space and has the technological, economic, and political will to do so. And also having self-replicating robots that actually succeed at their mission.

This would be miraculously rare. Maybe something on the order of one in every few thousand galaxies has such a society. There's no guarantee that even we humans would be able to achieve that.