>>714468705
>>714470816
Quite straightforward.
Every branching decision creates and new multiverse
Every bad decision or new fear creates a dark multiverse
Dark multiverses are destined to be destroyed when their stories play out.

That's why The Batman Who Laughs recuited the different Batmen to make the Dark Knights.
He went to their multiverses just as they were about to die and told them their worlds could be saved.