The number of cars that experience -40F(C) in a year is something like 3% of all cars. In the US that number is more like 0.5%. And even within that 3%, the average number of days where cars experience that temperature is on the order of a 3-6 at most. We spend a lot of time worrying about edge cases.

Yep. I put a heat pump in my house last year. It doesn't function at all below "only" -30C and doesn't make economic sense vs my natural gas furnace until around 0C. I got it instead of a plain air conditioner only so I had a backup to my furnace.