In the abstract you are correct but in practical application, products sold as air conditioners and products sold as heat pumps are designed and sized very differently, resulting in different consumption/efficiency for the same home.
If you have a gas furnace to heat the house, then it might not make sense to pay extra for a heat pump that works in both directions (to heat and cool a house). So you would just buy a heat pump that works in one direction to cool the house, aka an air conditioner.
But if you buy a heat pump to heat the house, you might as well have the unit be capable of running in reverse to also cool the house (since you have no other way to cool the house).