"...a subsequent call came in to the operations centre that diverted (his) attention.."

I have the feeling that's going to be the bottom line here.

"Why wasn't any family looking for them?"

They weren't where they were supposed to be, and the whole area was very remote. The people who live on reservations tend not to be all that loaded up with good vehicles and lots of money for gas. And the sociological problems on reservations could have caused most of the people there to not even be aware they were gone.

As others here have said, when things go bad, it's usually multiple facets of it that go bad that causes life/death situations, and this was one of them. If they hadn't gotten onto the wrong road, if they hadn't slide off the road, if the cell coverage and cell phone conditions had been better, if the weather had been better, if the dispatcher had been having a slow day and been able to focus more on their situation, etc.

When things go to 'ell, the domino-effect can be a killer.

Sue