That's quite a leap you're making. One very strong counterargument boils down to simple economics: where's the profit motive in building a fleet of von Neumann probes to 'eat' every solar system in the galaxy? Who is going to pay for this effort, and what returns do they expect?

If it takes a million years to colonize a galaxy, then unless you plan to live for two million years you aren't going to see the full fruits of your effort.

As a race our attention span seems to be narrowing. As far as I can tell, despite or perhaps because of recent advances in applied science, we're actually losing our propensity to engage in multidecade R&D projects. The next LHC-scale project is going to be an almost impossible thing to sell to the governments that will have to agree to finance it, and it would take years for us to return to the Moon if our survival depended on it. We are most definitely not moving in a direction that will lead to the sort of expansionism you're talking about.

Edit: here's another thing, with regard to the absence of 'radio bubbles' from other civilizations. It's really, really dumb, from a technical perspective, to transmit RF signals that are distinguishable from background noise. It means you're wasting power and throwing away channel capacity.

Look at an HDTV transmitter on a classical spectrum analyzer sometime, and you won't see much in the way of coherent structure -- you'll just see a pedestal where the noise floor seems a bit higher than usual. This means that the 'radio bubble' is not a bubble, but two nested spheres with only about 100 light years of space between them. To observe emissions from an advanced civilization, we need to look at just the right time, between the development of RF technology and information theory. Otherwise we won't hear a thing.