Why Aren’t We Piping the Heat from Air-Con Compressor / Coolant Units to Heaters Yet?

Was wondering … why aren’t we piping the heat from air-con compressors / coolant units to heaters yet?

These units are transferring heat from the room or fridge to the coolant gas and onto the air surrounding the unit.  Go check out the back of your fridge or the compressor unit of your split-unit aircon in your house, the one sitting outside the house, and you would find the air around it warm or hot.

Can someone device a way to make use of this excess heat?  As it is, this heated air is either going to waste or increasing the temperature outside.  Granted, no heat is ever wasted, it is just transformed to other forms of energy … or loss to space, ie out of the earth’s thermodynamics.

Just wondering … …