No you're absolutely right, a poorly insulated home does not make any qualitative difference to a heat pump's effectiveness, you just need to buy a bigger heat

No you're absolutely right, a poorly insulated home does not make any qualitative difference to a heat pump's effectiveness, you just need to buy a bigger heat pump. I think the way costs scale is important - a big gas boiler doesn't cost that much more, you're just burning more gas, but a big heat pump costs more. Heat pumps put more of the cost up front and less down the track. So if the uninsulated homeowner is facing a $10k bill for a massive heat pump they can say "ooh what if I spend $1k on insulation" and they could get the sizing down and spend $6k. There's really no fundamental difference. The heat pump itself doesn't know whether you've got a massive house that's well insulated or a tiny house that's poorly insulated, it's just a heat load.