Sure, cold is a factor.
But would cold keep you from feeding your family, if you had few other options?
Laziness is a factor too, as Koblenz and newgeezer point out. Laziness will keep some men (and women) from feeding their families.
But you also have to consider the Bakken’s geographic isolation and the region’s ruralness. Williston, in the heart of the boom, had a population of what, about 12,000 prior to this boom, and was the fifth largest city in the state?
Billings, Montana, 300 miles to the west, has just over 100,000 people; Fargo, 400 to the east, is a bit larger, and beyond that you have to go to Minneapolis or Spokane to top 200,000.
The North Dakota countryside has emptied out over the years as the farms got bigger and the young hit the road. South Dakota is the same, as are the Canadian provinces to the north.
There just weren’t many people around when the boom hit, and there isn’t any housing for the ones who want to come now.
Well really all they need to do is provide the land and say welcome Southrons, just bring your double wide trailers with.