It's completely immaterial how old, mature, and technologically advanced some presumed alien societies might be. So let's presume that there's an alien 'empire' out there that spans tens of thousands of inhabited worlds and has existed for a million years. They've got faster than light travel. In which thousands of the 300 billion stars, in just our galaxy, are their thousands of inhabited systems? Then you have the stumbling block that I've already mentioned; they would have to stumble across us in the tiny fragment of time in which we've existed.