Cook isn't bound by that true enough, because he remains the majority stakeholder, but that is increasingly not the case as it becomes more and more regular that companies bring in new CEOs from entirely different companies if not entirely different industries, who do not own that much stake. In those cases, the board and shareholders can and do exert a lot of influence, up to and including firing them if they do not do their jobs correctly, which to shareholders is invariably some form of "make line go up."
And that's just civil influence, there are legal mechanisms indeed in place if a CEO "trashes a company" and what that means is different depending on the company.
And that's just civil influence, there are legal mechanisms indeed in place if a CEO "trashes a company" and what that means is different depending on the company.