Technology

I suspect it’s mostly a function of mass availability. Even here in the states ground source heatpumps are rare, even though the systems are more reliable (since there is no equipment exposed to weather) and a shallow borehole isn’t excessively expensive.

I’d forgotten about heat pump clothes dryers. Those are fascinating, and really interesting for older buildings or locations without close access to exterior venting.

Shallow geothermal is basically dead in most of the world because it's too much hit and miss, the geology is simply too complex and involved (and underground) to predict. There's also a fuckton of issues with water ingress, minerals that like to expand when getting wet and such. You can't really take Iceland as an example for countries not straddling a continental rift.

Deep geothermal is utterly reliable but for the longest time drilling that deep was just too expensive. Plasma deep drilling is a solution but it's still in its infancy.