I think the big picture is that you know there will be an average number of days per year when it will be below -40 and the aircraft won't be able to operate. You choose to deploy those aircraft anyway for business reasons. Then when it is below -40 you say it's not our fault we can't control the weather. However, you made a conscious business decision that it just isn't worth the extra costs and it makes more business sense to just shut down for say an average of 7 or 8 or however many number of days per year. If by claiming weather you don't have to rebook people on other airlines or pay for hotels then that just adds to the bottom line and helps your business decision.

Throughout 'you' refers to AC or whoever makes such decisions.