You are correct. In terms of fan efficiency, it is more efficient to force cool air onto or through a hot zone, than to draw hot air from a hot zone and expel it to the atmosphere.
With the external unit of split system air conditioners (heat pumps) you have to consider other things.
The current arrangement may be easier and/or cheaper to manufacture.
Also, under the current arrangement, the external units of split system air conditioners is compact and thus requires occupies less space where they will be located. Also, the fan is located at the front of the unit, away from the wall. When it expels the hot air from around the coil it does so freely, without any obstacles impeding the air flow.
For the fan to blow cooler air onto the coil two situations are possible. Firstly the fan could be at the front of the unit drawing unimpeded air from the atmosphere. It then blows that air onto the coil forcing the hot air around the coil to move. That forced hot air will have to negotiate any internal obstacles within the unit and could hit the wall of the building, which may restrict the movement of the air away from the air conditioning unit.
The other possibility is to locate the fan at the rear of the unit drawing in air from the narrow gap between the wall of the building and the unit, which is restriction to airflow, and forcing it onto the coil. Again, that forced hot air will have to negotiate any internal obstacles within the unit - a further restriction to airflow - before exhausting to the atmosphere, at the front of the unit.