It makes sense temporally. If you have a species that is intelligent and has the capacity to evolve to more and more sophisticated tool building, then that wil

It makes sense temporally. If you have a species that is intelligent and has the capacity to evolve to more and more sophisticated tool building, then that will build on itself. If life is so common that it has arisen independently on other planets in our solar system, it would be likely that these intelligent species would have arisen hundreds of millions of years before us. And even if most don't advance to interstellar travel, it really only takes a few expansionary ones if they were sufficiently long ago that we would have seen evidence. Again, if life is so common it is on other bodies independently in our solar system, this should have happened probably.