They advertise that make MORE money. To continue their brand. To stay in business. If they stop, they will go downhill.

As to SkyMiles program. They will continue to advertise. To the regular person, it looks like a good deal. Fly with us and we give you a free flight to Hawaii next year. Okay, reality is a bit different, but that is what works. Of course, they have made that concept complicted with MQMs, etc. Try to explain that to the average guy - you know, the yokel that continues to repeat "...better safe than sorry...." as he is herded through the security joke and thinks he is safer than before 9/11.