Technologically advanced civilizations in the galaxy may be short-lived because they inevitably destroy themselves, but perhaps extraterrestrials haven’t contacted us because they’re too introspective for space exploration:

One problem might be conflict resolution before they wipe themselves out. One problem may be a loss of interest. They might turn to internal religion, like Zen Buddhism, emphasizing the here and now.

From “The Lifetimes of Technical Civilizations” by Shklovsky, Platt, Stent, Minsky, & Gold in Communication with Extraterrestrial Intelligence (Sagan, 1973)