I have a theory that intelligence isn't particularly rare however the rate of development may be. It has long been alluded to in Sci-Fi that humanity's rate of development is fast (Humans vs Vulcans, Halo universe, etc). I imagine that one of the great barriers is that a civilisation with a lower rate of development may stuck in an industrial type era unable to progress before doing irreparable damage to their enviro…
Life shows up and spends a long time doing not much, then exponential growth kicks in, life gets smart and suicides out in 100000 years or so.
The rate of intelligent and communicating planets is going to be low enough; the chance of two such planets within a distance that allowed for bidirectional communication existing simultaneously is dwindling - and even then they'll be at different points in their growth curves.
If ever we meet aliens they'll be cavemen or gods.