> what I don't understand how these magical "sales people" apparently can't work for a fixed salary when literally everyone else can

It isn't that "sales people"[0] can't work for a fixed salary. The good ones just won't because they can find another employer that will pay commission, and they know they will make more with commission than without.

Employers will pay commission because that's how you attract the best sales people, and the best sales people are worth orders of magnitude more to their business than average sales people. Despite how much they earn, in general and compared to their average peers, the best sales people don't cost orders of magnitude more (5x is a more typical spread in tech sales.)

The advantage of 100% commission -- where it is legal -- is pretty obvious from the employer's view point. The company only pays for production. These sales people are commonly (but not always) independent contractors. The benefit for the sales person is a little less obvious, but, generally, they have more autonomy, a simpler comp plan without any caps, and earn more per dollar sold than they would on a base + commission plan.

0 - whether magic or not