People who manage game developers don't necessarily need to be good at developing games- they need to be good at managing people who develop games, which is related but not the same.
A CEO, especially at a larger company, does more than manage people. They influence the strategic direction of the company, and act as both public face and rolemodel.
While it's /possible/ for a CEO influence effective strategy without using or thoroughly understanding their product, it does not exactly inspire confidence.
People who manage game developers don't necessarily need to be good at developing games- they need to be good at managing people who develop games, which is related but not the same.