I understand where you are coming from but it doesn't work like that. Sales people are have direct measurement where the rest of us have proxy measurement. They also typically hold pre-existing relationships with potential clients. They take on more risk than any other side of the business except for executives (who are often former sales people).

But if a sales person performs wildly above what is expected of them it can change EVERYTHING for a company. Engineers are actually similar in potential impact, but measurement is a challenge... which is why we are typically paid higher than other cost centers in a business but why we are not on variable comp.