10. Outside Interference
If Superman and Batman did fight, there's no doubt that the entire world would be watching. The thing is, Superman is the guardian of the world. He has a lot of enemies, who ultimately would want him dead, and would clearly be cheering for the bat. You could say it wouldn't be unlikely for someone like Lex Luthor to interfere discreetly, so Batman can finish doing his job for him. After all, a world without Superman, is one much more vulnerable to villainy. You can't really make that same case for Batman, after all nearly all his villains inhabit Gotham. Generally speaking Batman isn't a huge threat to the world, and there are certainly ways around him, as he mainly guards his home-turf as opposed to anywhere else. But Superman? There's certainly a lot of reasons why a long queue of colourful characters would be begging for a chance to help end Superman's legacy.