The ants weren't "contacted" in the sense of being asked anything, but that doesn't mean they were undisturbed. The question is not why intelligent aliens way beyond our tech level haven't tried to talk to us; the question is why they haven't just happened to crush us underfoot in the course of going about their normal business.
Part of the explanation of the whole conquistador/ant analogy addressing that point is that maybe other beings travel inter-dimensionally or in some other manner that isn't what we take for granted to be the only logical way to get around the universe, big ass spaceships, those would definitely disturb our ant pile.
