usually there are lawyers involved when hiring a c-suite and there are negotiations and contingencies. if you fire a c-suite you might have to send them off with a lot of cash and/or legal fees. it might even cause a little stir in the public image and hurt the stock or investor perception. It might be cheaper or less of a headache to just work around them.

one of the better scenarios is to have a candid, open conversation about their offramp and give them a couple quarters to find a good spot somewhere else and then they "resign".