They became dumber, could no longer understand the technology that was keeping them alive, and died out.

Really, the only reason we are as intelligent as we are is because intelligence turned out to be helpful for survival. But that same intelligence lets us defeat our own survival instincts (which is why we have obesity, drug addiction, and porn). This suggests that for continued survival, either our instincts must become stronger than our intellects or our intellects must become weaker than our instincts -- both of which lead to the same place: exhaustion of resources before we actually accomplish anything.

(Disclaimer: I recently rented "Idiocracy".)