Power
The power of a director is deceptive. Technically, they're the boss. Everyone on a set takes their marching orders from him. If filmmaking is war, then the director is the general.
But, like a general, the buck does not stop with the director. Not only does he have to play nice with high-powered stars, but he has to answer to the producers, the investors, the studio....
In another type of business, the director would be upper-middle management. Most of the rank and file falls under him and he manages the project, but ultimately, he has a string of people to answer to. And make happy. And keep happy, if he wants to keep working.