Corporate executives are very protective of their self-image (when you’re already very rich, prestige becomes a most coveted asset) and their company’s brand reputation. Trump, whose popularity is very low among the populace and near zero in elite circles, does not reflect well on CEOs. Expect fewer and fewer executives to stand side-by-side with him.
Also, I wouldn’t be surprised to see the folks from Wall Street, K Street, and Big Business leave his administration. For instance, in his (unwitting) interview with the American Prospect, Trump confidant Steve Bannon explained how he is constantly fighting against Treasury Secretary Steve Mnuchin and adviser Gary Cohn, both alumni of big finance.