I don't think that is necessarily true.
You use the number 400 billion as if it is some extremely large and impressive quantity, when in fact, compared to the kinds of numerical quantities that exist in the infinite totality of everything, it's almost certainly infinitesimal. Or less.
Also, the conditions required to support life happen randomly. Galaxies vary in size. Therefore, there could be entire galaxies that have one or even zero star-planet solar systems where life could potentially occur, while other galaxies could have several. Hundreds. Thousands.
As for radio waves and radio telescopes, certainly they are right now the best (and only really), tool we have for scanning space for signs of intelligent life. But it's not perfect, as we have zero idea about what kind(s) of technology other worlds might possess, and of course, the distances involved between our world and other life supporting worlds could very easily be so vast, no radio telescope we could ever produce could detect it.
The bottom line is that we live in total darkness with regards to knowledge of what exists in the distant universe and any other intelligent life that might be out there somewhere.