also if there were a large space empire that was destroying planets and was wide enough to be an omnipresent threat, then we would probably be picking up their radio signals and communications all the time. why should they care about others hearing about them what are we gonna do run from our solar system also this doesn't make sense because there'd be no way for "new" species to learn of the giant space faring empire and thusly no reason to limit communications so this isnt an explanation at all