Why is a HWHP much more expensive than other standard electric or gas hot water systems?

Why is a HWHP much more expensive than other standard electric or gas hot water systems?

Heat pump water heaters are highly efficient and use 30% of the energy of a conventional electric hot water system. These systems use a refrigeration cycle to extract heat from the air to heat the water, like a split system air conditioner, so the cost is similar.
Heat pumps cost more than a conventional electric HWS but are much cheaper to run.