Or they're not communicating using EM. And maybe they can't get off planet. And maybe the mean distance between pairs of civilizations is so large that interstellar travel is just not practical at all for any of them and us as well.
The errors in history have been the opposite: believing other intelligences are more common than they have turned out to be. The world was filled with non-human creatures in mythology and folklore. In the 1700s it was presumed every planet in the solar system had intelligent life on it.
If it’s vanishingly unlikely, but space is incomprehensibly huge and time is vastly long, then it happening exactly once is extremely improbable. 0 times, believable. But those probabilities yielding 1 life event must mean 2 life events is also possible, no? Or 3? Or 100? Why so confident it’s exactly 1?