Just like you can book a Virgin airlines route via Delta.
Getting tickets for a flight on any airline uses a booking system.
https://en.wikipedia.org/wiki/Global_distribution_system (optional) vs
https://en.wikipedia.org/wiki/Airline_reservations_system (required)
Delta offers two types of inventory - regular inventory and “award” inventory. Award inventory is only available to alliance partners, is very limited and you can only pay with points.
You can’t even buy the flight at that price with Delta Skymiles.
For instance, I can’t pay cash even if I wanted to and get a discounted price for the flight in question via KLM. I have to use points. Those prices aren’t available via online booking systems.
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
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.
I don’t have a choice if I want to fly to see my parents since that’s the only airline that services their airport.
But a more popular route I take is from Orlando (MCO) my current home to my former home Atlanta - a Delta hub. Those flights range from $100 to $175 one way. Again by booking Delta flights through Virgin (a UK airline) is 7500 points making the Amex points worth 2 cents each. If you want to fly direct to or from Atlanta, you’re going to fly Delta more than likely.