After a discussion – or rather, the two bigshots discussed, and Victor minded his own business – Superman finally didn't take action.
That was because Master Wayne had said very calmly, "Nobody knows the Joker better than I do. If you take action directly, you'll only step into his trap, and the consequences will be even worse. Then, you'll realize that you're being forced step by step into a desperate situation."
Superman couldn't say anything in response.
That was because Gotham was Master Wayne's territory. Given the tacit understanding between the two bigshots, they rarely stepped into each other's cities — this was mainly when it came to fighting crime; there was no problem in Superman saving people around the world.
On the other hand, law and order in Metropolis was clearly much better than in Gotham, and the people at the bottom were at least several times happier.
