Directors are more apt to take action when an employee blows the whistle -- and when their companies therefore are subject to bad publicity.
If there are many employees that know about the executive that has had sexual relations with many female employees they would probably annonomously feed the info to the directors.
How would you feel if you owned stock in a company and they allowed this to go on.
Maybe having sex with your employees is allowed at some companies but it seems that if a company had a policy where one of the top executives was able to use his position to have improper relations with multiple female employees they would have a problem with this. Especially the direct reports.