It isn't just that. Our focus on the search for ET's signals has mainly focused on the 1 to 10 GHz frequency spectrum. One of the reasons for that is that above 10 GHz the universe gets very noisy. Signal to noise ratios would be very low. It becomes very difficult for us to discern them from the noise so we don't expend much effort looking for this type of signal there. Other civilizations could be communicating via frequencies we don't monitor such as ULF.
But like I said, I believe the main reason we haven't detected signals from other civilizations is the distribution of advanced civilizations in space and time probably makes us the only one there is in this area at this time.
Here is one for you. The pantheists could be right. Our universe is god, and the noise we hear from space could be god's own thoughts. Thoughts we are interfering with by broadcasting reruns of I Love Lucy. If so then contrary to the hopes of theists like Drew we aren't the end goal of existence but rather a parasite causing concentration problems, and all the broadcasts of The Donald lately have probably caused a hell of a migraine.
I know about the frequencies, and I know the Drake equation.
I see a couple possibilities here.
1. Extra solar travel is simply not possible for a variety of reasons.
2. Every galactic civilization never finds another.
3. We are utterly unmatched in time.
4. Every emerging space civilization is immediately killed by advanced ones,
5. Space-faring civilizations are rare.
6. We are the first or only.