The Universe is very large, and all theories may have something to do with it. But it is equally likely that, although very common, that life is not close enough to our Solar System, or even, that they have not yet developed enough, or that they are already extinct (it is not simply a matter of space, if not also of coexistence at the same time).
In one way or another, the explanation to try to answer why we have not found other intelligent civilizations is fascinating (in both ways).












