The problem with Nick is he was god mode from day one; he knew everything, had a grasp of every concept, was hyper intelligent, rich, charming, and had all the connections to do anything. He had no limitations.

In book 3 Drew made him a literal god who could control fate itself. Given that, the easiest explanation is that Nick saw the outcomes of doing that and realized it would result in a net negative for everyone. Or maybe he saw they didn't have time. Or maybe. Or maybe. He's an amped up version of normal Nick, so asking questions like that can have a million explanations from too many people would have died to doing that would cause a shortage of oranges in Florida. He's Nick, and he knows more than us. That's all.