Wonder if it was a hotbox. There is a pretty long stretch where they go between detectors there. Because the sidings and setouts on both sides of Flathead tunnel are arranged such that it would require a train to occupy the tunnel to make a setout from somewhere deep in the train, they arranged things so there is no westward scanning at the detector on the east side of the tunnel, and no eastward scanning at the detector on the west side.
Heading west, there is bidirectional scanner at Olney, MP 1236, then an eastward-only scanner at MP 1258 near Brimstone, Flathead tunnel is between MP 1265-1272 (7 miles), then a westward-only scanner near Wolf Prairie MP 1277, then a bi-directional scanner near Fisher River MP 1296.
For a westward train such as this one, it would run from 1236 and through the tunnel to 1277, between hotbox detectors. This one apparently derailed around MP 1272, 5 miles short of the scanner at Wolf Prairie.
I can understand the crew safety reasons for not wanting to do setouts at the sidings near the tunnel, but I wonder if the long distances and probabilities just caught up with BNSF on this one. Its not uncommon for trains to have to wait for tunnel ventilation, so some trains do have the opportunity to cool their heels, literally, which mitigates the lack of scanners a bit.