I was unaware of the tipping issue, but that makes sense. Seems another option would have been BZN (Bozeman), where DL does regularly operate 739s to SLC and MSP. BZN is roughly the same distance from the diversion point as GEG, but would have allowed the flight to continue in the same direction instead of backtracking. I wonder if the time of day (or night) and the level of staffing on the ground at that hour had something to do with it?