I found this:
There is more than one organization the regulates how airlines (and other companies) account for future liabilities: FASB here in the US and IFRS ... elsewhere. They have never managed to say definitively _how_ airlines should recognize on their books the liability of mileage programs (by contrast, for example, there are rock solid rules for how companies recognize vacation benefits for employees, which is why if you leave a company with a balance of vacation owing you, you get money, and if you were allowed to use more vacation than you had accrued, it will be deducted from your final paycheck -- or you'll get a bill). The method _I_ was familiar with basically says, meh, no one was gonna by that seat, so it's only value is the cost of the meal, snacks and bev we were gonna serve, and whatever additional fuel a 150 lb person and their luggage requires for the flight, aka incremental cost. The method that was the alternative, and which airlines exiting BK have been opting for over the last decade-ish, however, (deferred revenue) treats the initial purchased tickets as two components: you are buying the fare you are buying, and you are buying the mileage bonus. So when you actually _use_ your points, the airline "recognizes" the revenue, moving it from its reserves to its income.
This is also known as "income smoothing". Now, on the one hand, everybody likes income smoothing -- that is why way more people work for a company that can provide steady hours and income, vs working for themselves and dealing with periods of crazy overload interspersed with terrifying droughts of no income. On the other hand, everybody _hates_ income smoothing, because it suckers people into investing in fossilized companies that have been living off their reserves for quarters or years and appear on paper to be a going concern but once the reserves are exhausted there will be absolutely nothing left because there is no actual new business. In this situation, an airline that during an economic boom time used the deferred revenue method would built a pile of money that, during a period of economic slack, they could transfer on their books as "income" while running planes full of exclusively awards fliers. On the good side, at least the point flyers are not displacing people who would have bought the seats with folding Euros or green stuff or whatever. On the downside, an unwitting investor might think that all those flights full of fliers meant the airline was a going concern, when in fact, it was just running down its reserve balance.
I don't know. I look at points programs and I go, too much sugar for a penny. I particularly despise the effects of incremental cost, because the drive to reduce the impact on airlines of rewards flyers means that everyone now has to pay for absolutely everything separately: no free bag, no free lunch, no free anything. But the potential bad side of deferred revenue, especially in the absence of appropriate regulation of reserves, is terrifying. Can't you just see it? It would make corporate raiding of pensions seem like chump change.
And then on top of it, all the credit cards and so forth that pay airlines money for the right to distribute awards points in exchange for running up huge amounts on credit cards are trying to tell airlines how to manage their FFPs -- leading potentially to a day where points fliers occupy all the seats, and if you want to fly, you'd better get and use an affiliate card or you don't even have a chance at flying for any amount of cash (this is the situation that caused me to buy into DVC -- you _can_ get me to play in an insane voucher system, if the good on the far side is sufficiently desirable) unless you first convert it into points.