The short of my theory is a civilization that advances too far down the tech tree gradually is effeminiatized by more and more technology and steadily grows more decadent and libtarded until it collapses. I think there might be something to it...especially with recent events.
We tend to think our technological civilization will last forever. However, it is barely 100-250 years old (depending on when you start counting), not even a blink of an eye. There is no guarantee at all that intelligent beings will remain intelligent. A lot can go wrong. It is quite possible that intelligence may only be apparent for a few thousand years before it is extinguished.
It is also possible that being may become sufficiently advanced that they become machines or Gods that transition into another phase of existence. Lots of people also postulate we are living in a simulation. Much good SciFi has been written about all these possibilities.
So if each of those civilizations only lasts for a few thousand years at most, its easy to see how they could miss each other.
Many sublime ...