Is because intelligence would only benefit a eusocial species. As it stands, complex and unified society on the scale required for achieving the feats of engineering, both in efficiently harnessing resources, and in developing the knowledge to achieve these feats, is impossible. Genetics has wired us as a species to compete and favour the individual over civilisation. Mathematically the optimum strategy for any group is Always Cooperate. Nature shows evidence for this: eusocial insects are the most populous and successful form of life on the planet.
By the time any species learns the benefits of cooperation, they may well have managed to deplete their natural resources beyond the point they might be put toward interstellar travel and communication. The other possibility is that no intelligent species has yet developed to the point of being able to achieve these things, or if they have, they're too far away and haven't reached us yet.