It’s a question of temperature difference. Cooling a house from 40° to 20° uses approximately the same energy as heating it from 0° to 20°. But it gets much colder than 0° C in Finland, while it is very rare to have temperatures above 45° C anywhere in the world.
It's not just that. To make something colder using a heat pump, you must heat up something else by the equivalent amount. Actually more, because of losses.
Whereas making something warmer can be done without a heat pump, by releasing stored chemical energy, at nearly no losses.
Ductless heat pumps are more efficient at heating than alternatives, but there's a floor on how low of an ambient temperature they can handle.
Heating something with chemical energy by combustion (for example) has a large second law loss -- there's a large increase in entropy in combustion, and in transmitting the high grade heat to the low temperature of the building being heated. Because of these avoidable entropy sources, it's possible to be smarter, for example to use a gas-fired heat pump to achieve a COP of > 1.
Yeah, a simple absorbtion refrigerator (gas fired) is already way better than a gas oven.
The plumbing is just more expensive than works often be worth it, and the nice low-temperature systems run on what's essentially an ammonia destiller.
How much does construction affect the efficiency?
Heat pumps are more energy efficient than resistors, so I guess it depends on the method.
Nope, it’s all about the temperature differential. Using a heat pump like an air conditioner is the same efficiency either direction. Usually when you’re talking about heat it’s going from (say) 20F to 70F, with AC it’s more like 90F to 70F. With heat you might even need to do like 0F to 65. AC max might be 115 to 75 which is still substantially less.
How about building design? I know in colder climates buildings are designed to retain heat. Are buildings in warmer climates designed with similar heat insulation in mind? I think traditional architectures are designed for convective cooling but that doesn't play well with air-conditioning. Not too mention the modern designs obsessed with glass which I think traps heat. Good and efficient for cold climates, not so much for the hot ones.