Krypton TV series trailer screencaps: Kandor
So Superman is usually shown living for millions and millions of years. Why not Supergirl or any other kryptonian that's ever shown up? But that brings me to my next point: What if Krypton was supposed to be the source for the Fifth World? The next wave of gods for when New Genesis and Apokalips fell, but its premature destruction extended the age of New Gods artificially. Like if you could knock out the four horsemen before Judgement Day.