They are used a lot in hot climates but from what I heard, they aren't very efficient in cold climates.
Either way the capital cost of a heat pump is high and people seem to have a psychological aversion to spending money on capital costs.
One of the best selling points of a heat pump is comfort: it switches continuously from heating to air conditioning. An eco-sensitive person in Upstate NY might not really think they need air conditioning. It's not like buying a Toyota Corolla to save the planet, it's more like buying a Cadillac Escalade to save the planet and the psychology doesn't really work for that.
See https://energysavingtrust.org.uk/air-source-heat-pumps-vs-gr...
But in places like Florida, if you have a 15+ year old A/C, replacing it with a conventional modern heat pump, it would probably pay for itself in a few years.
Plenty of places get or stay colder than -25C, but that is often short stretches or overnight. There are a lot of places that would do better with a little resistive heat backup compared to the huge installation costs for ground source.
New neighbourhoods in cold climates should be required to install community ground source heat pumps. Since all that dirt is moving anyway the cost of trenching is negligible and any drilling is amortized over many properties.
Heat pump capital costs are too high. They should be standardized or designed to be cheap and used everywhere…to recover waste heat from everywhere in the home.
Ground source is expensive, but that's due to drilling and/or trenching. The actual heat pump is a tiny fraction of the bill to install ground source heating.