Let me put it another way.

Salespeople are currently useful solely in counteracting the effects of other companies' salespeople. If all salespeople were removed from the earth (and no new ones popped up), everything would still move along fine. Probably better, as people would make purchasing decisions based on actual technical merit.

Contrast that with a profession that is almost always seen as a corporate burden: IT. IT makes no money for the company, but if all the IT staff was removed from every company in the world, the computer systems would go to hell in a handbasket before any time at all.