GFK DEN failed because the Northern Red River Valley has a disproportionately large number of high value Delta (NWA) frequent fliers. They where not switching to United when they paid a little more on dl but get free bags free upgrades and free ticket changes. When the only time the Denver flight was full was when a big sky team flew in the. When united just randomly started canceling flights for aircraft to be used other routes the writing was on the wall.