I like this one the most: "It is the nature of intelligent life to destroy itself"
There could simply be a technological ceiling. Once civilization reaches the ceiling, it hits it's head on the ceiling, and falls down the stairs either destroying itself or at very least losing most the progress.
There could simply be a technological ceiling. Once civilization reaches the ceiling, it hits it's head on the ceiling, and falls down the stairs either destroying itself or at very least losing most the progress.