Obviously, employers are not going to operate a business at zero profit margin, so I am not sure what the significance of pointing out that employees do not get paid the sum total of their economic contribution to a business’s profits (which I imagine is rarely ever calculable).

The whole point of having buyers and sellers engage in numerous, transparent transactions is to figure out what portion of the business’s operations should be allocated to the purchasing of labor, since there is no objective way to measure it and have a definitive answer. It is always moving, and needs to be continuously updated. The same reason employees always need to be shopping around and seeing who will offer them the appropriate price for their labor.