Here's the deal. I'm not a big fan of Bob Iger, but I think he is a shroud business person. He knows to follow the money. That said, every project James Cameron has gotten personally involved with made tons of money for the studio that contracted for it. There is no exception to this rule. And we're not talking some money, enough money, or good money. We're talking obscene amounts of ridiculous money. And each project just doubles in the amount of money coming in, compared to the one before.
That's why Iger signed up for it. It is, however, sad that Iger couldn't find that kind of talent within his own company. His track record has been to go out and buy talent (Pixar, LucasFilm, Marvel, LightStorm) instead of incubating it from under his own roof.