Why do people in the "entertainment industry" and "top sport" have higher "base-salaries" than CEO's? How is this justified in business terms?

Because they are the demanding personalities by the people..

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When you have millions of followers on the social networks and your marketability is very high, then i believe you are worth much more than what you'd get as a CEO beacuse you are looked at as a brand/product and an investement that will lead high ROI for your sponsors/agents. 

i believe sallaries are determined by each industries rate of return on investments which translates to the profitability of the industry.

entertainment industries and top sports are highly profitable industries and they can afford paying high wages or sallaries.

the ceo's you mentioned might not be in a highly profitable industry,and if they were athletes or stars are the profit generators and of course they deserve the higher pay due to their high yielding performance.

an actor will bring success to a movie just because of his participation,he is adding great value and deserves the credit.

Because entertainers and sportsmen are reaching, connecting and selling to the millions of people with their skills. They represent a brand and their popularity represent their value. In return entertainment and sport companies who pay their salaries in millions earn tenfolds. 

CEO could earn the profit share from the organization which is indirectly the efforts of employees.