I strongly suspect that worlds that can actually support the creation of life are incredibly rare. Exactly the right mass, exactly the right temperature, exactly the right amount of liquid water and tectonic action, sufficiently strong magnetosphere, sufficiently stable solar system, and so on.
And then the creation of intelligent life is going to be orders of magnitude rarer than that, and spacefaring life orders of magnitude rarer than that. It's not as though a race of intelligent space dolphins would be likely to discover fire, and it would be pretty challenging for a species on a gas giant to develop space travel.
Furthermore it looks as though we are pretty early in the period when the universe could possibly create complex lifeforms (relatively speaking), owing to the lack of atomic diversity in the first few billion years after the bang.