The famous Douglas Adams quote is relevant: "Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space."

The odds of an alien civilization picking up one of our probes, even if we send out thousands of them, is preposterously small. Imagine trying to such an object if it had been left floating at an unknown point in the ocean; now consider how much bigger interstellar space is than Earth's oceans.