You know, just because people survived the earthquake doesn't mean any of the survivors knew how to work the technology that was around. How many people these days can't work a simple computer? If most of the scientists and engineers died then how would the normal people know how to operate the more difficult equipment or even repair it if needed?

These people lived without having to do anything at all, everything was provided for them. Do you really think they would have the knowledge to restore their empire? Instead they all likely spread out across the world and joined other groups of people and learned how to survive. Even if some of them could repair and work the technology, they might not want to due to the fact that it annihilated their empire. They might have been against using such dangerous technology and instead wanted to effectively reset the world but having the story of their destruction passed down to keep their descendants from repeating their mistakes (for when they start advancing technologically).