10 Theories Why We Haven't Discovered Aliens Yet
2. The Great Filter
Maybe Earth isn't the first, or rare, or has been doing the right form of communication, but it doesn't matter, because every other life form that has ever existed in the galaxy is dead, and has been for a long time. That's the Great Filter Theory; there comes a point in a species' development that they experience an extinction event, and they are wiped off the map.
Earth has experienced five (and is still undergoing a sixth), and humans have managed to come out of them, either through blundering into the right place at the right time like a species of Forrest Gumps, or some natural advantage we didn't know we had. However, if Earth was successful beyond all other planets, then that means much more failed. Perhaps Earth passed up the Great Filter years ago. Or, the more unsettling part of the theory, that Earth hasn't passed the filter, but every other species has, and it will hit any day now. That might just be worse than being stalked by 4-dimensional creatures.