> They just need to use reverse-cycle airconditioners to efficiently heat the air and dehumidify it instead of simply using a resistive heater. These are much more complex to make and are expensive.

I've seen these in apartments in Europe; I presume this is because it's a PITA to route a dryer exhaust vent to the outside in a 400-year-old building with 2-foot thick stone walls. Such dryers work well; you just have to dump the accumulated water out of them every so often. But I've never seen one for sale in the US.