Here's my idea: (which is for the most part, Marvel-based)
In an alternate dimension parallel to our own but entirely different existed a being simply known as
Mojo. This foul creature had dreamed for one thing for as long as he can recall, this beings one true wish was to create the most exhilarating and action packed drama series to ever land on a television. This desire gnawed away at him, driving him into insanity as he tried over and over again to create this fantasy of his. After thousands of attempts Mojo decided he needed help, something more to make the entire thing easier. When knowledge of the Infinity Gems reached Mojo he knew their power would grant him what he desired so much. After years of scouring and scheming, Mojo collected the Infinity Gems and forged an ultimate weapon known as
the Infinity Gauntlet. With this fantastic item Mojo took the two most thrilling timelines he could find and mashed them together. Streaming to millions of alternate timelines, the events that unfold in Mojo's world will be witnessed by more creatures than any single event
ever.
I figured the entire world would be imagined by Mojo. Places like Spider-Man's New York, Batman's Gotham City, Latveria, Atlantis all exist on the same planet somewhere. It is inhabited by every human any of these heroes could know and some that don't, although they are simply created by Mojo and not actual people meaning their existence doesn't truly matter (although the heroes don't know that.)
I dunno just spit ballin' here. I don't know much about DC if I'm honest.