Insulation obviously also helps keep a place cool. But no amount of insulation will ever remove the need for cooling if the outside is warmer than the inside. Energy is always going to move from a hot place to a cold place, but at least insulation lets us control how quickly that happens.
Also the limit on air sourced heat pumps in cold conditions is basically caused by water freezing on the evaporator coils, effectively adding a layer of insulation that limits how much energy can be drawn from the air, we’re not really limited by the refrigerants. As other have mentioned you dig down to find a better source of heat, and often you don’t even need to dig far, a 20-30cm trench is often enough. Although in super cold climates you’ll need to go deeper to make sure your through the frost layer in the winter.
I thought any place that is significantly cold can still dig underground and at some point you can get enough heat to run your heat pump?
Some people on reddit are reporting quotes of 125k for larger (>3000 sq ft) houses.
As someone who lives in a 4-season environment that can get down into the single digits F on occasion in the winter (forecast to be there for a couple of days next week), and has an air-source heat pump, I just suck it up and eat the $400-$500/month heating costs for the auxiliary (electric resistive) heat in Dec/Jan/Feb. If someone gifts me a ground-sourced heat pump I'll gladly accept, but I've got kids to raise so setting aside money for one is a long way off.