Very few people live there: http://sedac.ciesin.columbia.edu/downloads/maps/grump-v1/gru...

The population and population density in those areas are incredibly low.

At least on the Canada side, the only two major cities in that area are Edmonton and Calgary, with a combined population of less than 2 million.

That's not true. Edmonton and Calgary have each been over a million for a while now. Alberta has also been the fastest growing province for probably a decade now.

Also Denver/Boulder and SLC on the US side are not exactly low population density.

Probably from http://en.wikipedia.org/wiki/Rub'_al_Khali