They're staying stchuum cos we are still barbarians
They're still making their first tentative steps from water to land (or their equivalent of)
They haven't noticed us yet which is perhaps a good thing because they're bloodthirsty planet conquerors with far superior weaponry to us
They know we're here but we're boring
They're too far away
or
Actually, we're all alone as the only beings with the ability to reason in the entire Cosmos.