KCFlyer,
Because airlines are stupid, for the most part. They realize that the fare structure must change, yet when one airline attempts to do it, they CMI that carrier to death and force them to pull the fare changes. It's ridiculous.
But it is not so easy to simply restructure revenues. There are reasons why HP has been successful in their fare restructure. As I keep pointing out, their CASM is 3 cents lower than US Airways. That is a HUGE difference. So it's easy for them to offset the net fare change by increasing load factor. With US Airways costs still north of the 10 cent range, there is no way they'll achieve enough load factor increase to offset the net fare reduction. They'd lose revenue, not increase it. It drives me nuts when people say just increase revenue. Do people realize how hard it is to do that? It's not like all of these airlines are simply sitting on their hands and doing nothing. They are trying things each and every day. But the big problem with changing fares is getting everybody to play along. NW is the prime example of an airline that has been unbelievably aggressive in driving back other airline fare changes. They fire off CMI's constantly! Why do they do it? Because their situation is much better relative to US, UA, AA and others. So they can afford to play hard-ball, even if what the other airline is attempting to do is good for the industry as a whole. That is but one insane way that this business is run.
US is going after more cost because it's about the only thing they have control over. They have no control over revenue. Their CASM simply isn't low enough to generate increased revenue with a revamped fare structure.