> If the roles are both equally necessary, why does the CEO make so much more than the secretary?
Most jobs don't set salary based on the necessity of having someone in that role, it's usually based on how difficult it is to find a capable person in that role.
If there are 100k people capable of doing the job of the secretary, and 5k people capable of doing the job of the CEO, then the CEO will be able to negotiate a higher pay rate.