Batman is just an imaginary character thought up from Bruce Wayne to deal with the physiological trauma of losing his parents. Everything in the DC universe that ever is or was exists within Bruce's head. Think about it.
>Villains are all baced on Bruce's childhood experiences and nightmares which explains why they are goofy and childish (a Ventriloquist gangster, an evil clown, a giant crocodile man, a man with a deformed face, etc.)
>It's why the DC comics continuity shifts and changes over the years, Batman doesn't always stay the same simply because he is a figment of Bruce's every evolving imagination
>It's why cities like Gotham and Metropolis have weird sci-fi architecture. From the perspective of Bruce, Batman is him all grown up in the future. What does a little kid think the future will look like? Clearly everything will be advanced and crazy.
>Characters outside of Gotham are likely based on people he's interacted with before (flash is maybe a track runner, superman is maybe an athlete who is a bit stand-offish with Bruce, etc.)
>it's also ultimately why Batman is never supposed to kill. Only a young child would be naive enough to believe that only punching bad guys and not killing ANYONE could actually work.