Gold is rarer, than oxygen and carbon. The market prices it higher. Does that mean it contributes more? Is gold more important than oxygen and carbon?
Sure, there needs to be an incentive to work hard. But there shouldn't be an incentive to being born in the lucky circumstances that leads you to becoming a surgeon, or the even luckier and more exclusive circumstances that lead you to becoming a CEO (white, male, relatively privileged). And why does a CEO who works hard 80 hours a week deserve more than a janitor working 3 jobs 80 hours a week just to keep her family afloat, to get her kid enough food and a safe place and help her get through the crappy public school that the CEO pays $30-60k a year (multiples of the janitor's salary) to keep his kid out of?
There shouldn't be an incentive to treat people as commodities. Does a surgeon deserve twice as much if for whatever reason there are half the number of surgeons this decade compared to last? Does a janitor deserve half the pay just because the birthrate increased and there are twice as many people to compete against? (I'm simplifying. It's not important whether doubling the supply halves the price.)