If your top salesperson commits improprieties, well then.. you still have to keep him. Clients! Contacts! Secret Sauce!
If your CEO is AWFUL, then the board can tell him he's fired. But if he's in process to sell the company? Well... sales is tough, might as well let him stay to finish it out.
One success can also change everything for a salesperson. John Thain received a ton of criticism... but he was able to sell Merrill Lynch for $50bn during the crisis.