The points steven b makes about information asymmetry are quite true, but isn't the argument largely irrelevant because the airlines control the number of seats allocated to each fare bucket and award bucket? Once they have decided how many seats will be sold at each price, don't they want people to find out? And if too many people are finding out about cheap seats or award seats or upgrade seats, can't they just reduce the number allocated to those categories, in favor of the expensive seats?

Maybe the (hypothetical) problem isn't that airlines don't want you to see what's available for you as an individual to purchase, but that they don't want you to see how much is available, i.e., how many seats have been allocated to each bucket? For example, in Southwest's newly crappy FF program, they won't reveal how many award seats are available on each flight, so you can't quantify exactly how crappy their program is. Likewise, because their system is closed off from other GDS's, when they advertise a fare sale it's impossible to know how few seats are actually selling at the cheap price.