Fun fact (well, I suspect you know this already, but some didn’t, I had discussion with someone arguing with me that this is not true):

AC and a heat pump are basically the same thing, AC is just pumping the heat outside instead of inside.

Also when you say modern cars I am assuming you might be talking about EVs. Using a heat pump requires less energy than using resistive heating so it could be energy saving measure.

ICE cars on the other hand can get the heat from engine “for free” (not really, but since the heat will be produced anyway whether you use it or not, so why not use it?) so a heat pump might make a bit less sense in them.