They didn't necessarily have, chronologically, the huge long empires and history wee see in Superman Beyond, they just have to have the story of it, the idea. They're addicted to believing ideas are true; hence Mandraak coming back/being again because they can't comprehend Mandraak's inherent fictionality. Monitor, in Crisis on Infinite Earths, kept doing stuff like this; the new Doctor Light, or Harbinger and Pariah, arguably (as bolstered by Final Crisis) even Antimonitor are just ideas that are real. Monitor's Crisis on Infinite Earths plans were pretty much a) pick some characters, b) make them do stuff, and c) when one turns out not to be as useful as previously thought, put them away and focus on those that are working. I doubt that was intentionally a metaphor for writing, but it is a pretty good mimic of what writers on titles like these do.