They are not and never have been. They have always been paid what someone is willing to pay them for the work they do.
It's subtle but important distinction.
Salary is a function of demand and supply like any other price on an open market.
This is why its important to not think in terms of work when negotiating a salary. Instead you need to think in terms of cost to find someone to take your place.
If that cost is more than your salary, you can ask for more.
