Yes, these are alternative explanations. The explanation that is surprisingly undermentioned is the one I put forward: there is no life.
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?
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.