I will say, no one's preventing you from making such an app for one of these Gotham-based characters...

...but yeah, in the past, there have been occasions where EVERYONE flocked to either Gotham or New York, and it does bare mentioning once we start getting a number of people all expressing intent to base out of there.  Especially early on, before numbers round the game out.

It's a fine balance.

Just like it's worth mentioning other characters exist when we start these games and we get four apps for Spider-Man, five for Batman and only twelve people total at that point expressing any interest in the game.

There's a difference between raising the point and giving a hard no, though.  Feel free to give it a crack.