Talking about alien life is the same as ghosts or true love: always talked about but never (seldom) seen.

Anyone subscribe to The Dark Forest Hypothesis? That is one possible explanation to this paradox.

Well there is a lot of (dark) matter we can't see, and don't know what it is, that limits our observation. Intelligence may be so big and vast that we won't know that we are actually living inside it, like a bacteria inside a human gut.