Management’s job is to “Make Sure.” If you don’t care if people are coordinated,or if communications are made, or if the important goals get done, then you probably don’t need a manager. !
But most places do care, and so they have a manager. Good thing for me, since I don’t have the technical abilities to be a Chanchai or a Sarawut, nor do I have the patience or the numerical precision to be a financial guy like Piya etc etc.