Random thoughts...

so like, why did no one just move out of gotham? https://c.tenor.com/eAqD-5MDzFAAAAAC/mai-sakurajima-sakurajima-mai.gif

Same reason no one moves out of a ghetto. Besides if the citizens move so do the criminals. In fact one could argue 90% of the citizens are already criminals. Then you have to factor in Metropolis isn't much better. The majority of the DCU is always under attack by some intergalactic planetary force. So where are they realy supposed to go? The multiverse? Have you read Final Crisis? Those universes are all dead! Then one says, "why not escape into the Marvel Universe?" only to realize that was rhetorical because their entire continuity is ruled by a mouse tyrant know as Mickey! The very same mouse that has already conquered our own reality. And furthermore might I remind you about our own existence in this bleak real life world. Let's face it Lamby. It's already too late for salvation for Gothem. They were a broken people before they had a chance to know it. @momoichi

Hypothetically they could go to the marvel universe it's happened before and at the end of that event the two universes fused creating one universe for a couple of comics until they unfused i forget exactly how it ended