> The booking systems you are referring to are based on paying cash and have all of the airlines inventory available.

Every ticket goes through a booking system. Not every ticked goes through an online booking system.

> I can’t pay cash …

Again I agree, you don’t have the option. That doesn’t mean nobody can get discounts. KLM also offers a military discount etc.

Or just look at their fees, a classic case of price discrimination:

  Cancel a ticket through the online refund request form USD 30
  Change or cancel your ticket via phone reservations free
  Change a ticket via an airport ticket office USD 25

https://www.klm.com/information/legal/fees-paid-options

The airline industry charges people setting next to each other wildly different rates.

PS: Jumping through airline miles points is worth X$ to you, they aren’t worth X$ to everyone.