Airline miles are a product sold to banks, not just a gift for frequent flyers.

A loyalty program can be a second airline business

A bank does not buy miles merely to give customers a perk. A co-branded credit card uses the airline’s name and rewards to attract spending and keep cardholders using that bank’s account. The bank pays the airline for batches of miles; the airline, in effect, sells access to a reward that can help make the card more appealing.

That exchange can be unusually valuable to airlines. Selling a seat means operating a flight, with costs such as fuel, labor, aircraft and airport fees. Selling miles does not require the airline to put a passenger on a plane at the moment of sale. The airline can earn substantial cash from its loyalty business even when the economics of carrying passengers are tight.

The cash arrives before the reward is used

The airline is paid when miles are sold, but it has not necessarily completed its side of the bargain. A customer may later redeem those miles for a flight or another reward. Until then, the airline generally treats some of the sale as an obligation to provide future rewards, rather than as money it can count immediately as earned profit.

When a member does book a reward flight, the airline must provide a seat. If that seat would otherwise have gone unsold, the cost of carrying the passenger may be relatively low. If it replaces a paying customer, the tradeoff is more costly. Airlines therefore manage award availability alongside ordinary ticket sales.

Why the points can feel less valuable later

The airline controls the terms of its program, including how many miles a reward requires and which seats are available. If an award price rises, a member needs more miles for the same trip. That can reduce the practical value of miles already earned—while giving the airline more flexibility over how much future travel its outstanding rewards will require.

So the cardholder’s points are not quite cash in a travel account. They are a claim on rewards under rules the airline can change, and the airline’s loyalty business depends on balancing that promise against the money it has already collected.