So for heat pumps to work in the northern parts of the USA (say, Minnesota/Wisconsin/etc) they cannot just be pumping heat from the air. They require geothermal loops.
So that's the two problems I described: weather a heat pump will work for your region of the USA is a complex issue. It's safer and easier to just pick a normal heating system. This uncertainty makes choosing heat pumps less likely in marginal climates like, say, Iowa. Of course this doesn't apply to places, like, say, Texas, which only get brief minor cold. Adoption of heat pumps there is straightforwards.
The follow on is that if you still want a heat pump in the cold parts of the USA you need a ground loop heat pump. And that has a very high initial capital cost, which means they basically only get put in during initial construction, not as add-ons to existing houses.
