^^ Nolan hired Zack. If Nolan was interested in directing the film himself...he would have done so. Snyder also originally refused the offer, he had to be convinced.
The director is probably the most influential person on a film production during the production and post production periods. The fact that you've now asked twice why everyone puts so much importance in the director...indicates to me that you have a lack of understanding how a film production works. Snyder is an accomplished and established film director...you may disagree with his films or dislike his style and that's fine...but to totally dismiss him is wrong. You just continue to overestimate the kind of power and control Nolan has right now. He'd be directing the film himself if he was interested in doing so. He's not and has long since moved on to focusing on "Interstellar".
Chris Nolan only did a few re-writes on the film...this is another thing that I've repeated and you've ignored. Jonah Nolan and David Goyer wrote the script. Even Zack's writing partner did a brief re-write I believe. So yes while Nolan does and has had considerable influence on the film, he isn't the all seeing figure you seem to think he is on this project.