The Drake equation? We can see the stars, we can see the planets (and there are lots of them). We can infer the number of earth-like planets. So where's all the intelligent life?
Does the drake equation takes into account the timeline earth-like planet have to be inhabitable to carbon-based lifeforms?
It could all still be at a relatively early stage like us. Grabby aliens hypothesis predicts this and models it quite well actually.