No matter the numbers plugged into any kind of equation to find the number of intelligent forms of life in the universe, as long as we aren't talking negative numbers, due to the number of stars the amount is going to be non-trivial.
If we accept that all interstellar travel must be at sub-light speed (based on our current knowledge and the amount of energy other forms of hypothetical travel would consume) trips to inhabitable planets--if they could be found--would take so long as to require a mortal danger to contemplate.
So, there are good reasons, based on our existing knowledge, why intelligent life has not covered the universe.
Besides, maybe, given a sufficient level of technology, terraforming near bodies is cheaper/safer than trying to reach distant, habitable bodies.