It's a comic book, I don't know what makes curses "lazy". Also the much more important factor is the deep corruption.

I say it was a process of elimination.

In a world in which heroes like Superman, the Flash, Wonder Woman, Cyborg, and Doctor Fate exist, your city has to be freaking cursed to keep getting all those cases of mental illness and corruption, keeping the city from really ever improving.

Organizations like the League of Assassins and the Court of Owls alone wouldn't cut it. Detective heroes would unravel their plans. Tech heroes would root their data out. Magical heroes would counter their spells, fast and strong heroes would weed out the thugs, henchmen, and mercenaries.
Eventually, it would get more under control, like Metropolis, Star City, Central City, or Keystone City.
They would need something so ingrained in the city that nobody can really ever remove it to get to the high levels of madness and crime you get in Gotham.

So at some point, a writer had to give up, throw their hands up in the air, and go "then... then... it's freaking cursed!"

And then you watch the God/King of Cities talk with the avatar Gotham (Stormwatch #3), and it's a freaking gargoyle talking about "the madness in me", while Paris and Metropolis are just human-like women.