That is my preferred explanation as well. A caveman would not notice a WiFi signal even if it was blasting right through the cave; he would probably be looking for smoke signals or something.
Also, a huge intelligence gap makes communication uninteresting. e.g. we know a little bit about how ants communicate via pheromones, but we're not trying to send "messages" to them; what would it possibly be useful to say?
Also, a huge intelligence gap makes communication uninteresting. e.g. we know a little bit about how ants communicate via pheromones, but we're not trying to send "messages" to them; what would it possibly be useful to say?