Heat pumps require a significant capital investment which would have to be recovered on only their efficiency improvement, since they don't otherwise generate revenue.
The math is different for new construction. There heat pumps make a lot more sense because the capital cost is relative to some other heating system you don't already have. Then the higher efficiency will generally cover the relative capital cost even if it wouldn't cover the total capital cost. This might still be less profitable than mining cryptocurrency (depending on a variety of factors) but better than any other traditional heating system.