And the employer wants to pay the employee as little as possible for as much productivity as possible.
In a perfect world with perfect information and rational actors on a level playing field, this is great: we expect supply and demand to converge, this is econ 101.
But it's not a perfect playing field, one side is coercive, holds most/all the cards, calls all the shots, treats people with lives and experiences as "resources", and seeks profit over all other objective functions. This is class dynamics 101.