Board of directors are like courtiers of old in a monarch's court.

They are there for the proximity to power. They scheme, connive, and work to improve their own position.

In the court of Zuckerberg, the courtiers exist at his behest, and his only. The directors who forget this are banished.

In other courts, the courtiers have more power because they can remove the CEO.

But even in courts where all of the power isn't concentrated in the CEO, heads can roll, and sycophants can be installed. Steve Jobs' return to Apple comes to mind.