How about lack of commonality & associated cost of spares. Very significant to the civil marketplace - less so to the military. There have been other multi-engined a/c with "handed" props - one that springs to mind is DH Hornet twin engined fighter of late WW2. It was only a twin but had LH and RH Merlins - well the engines rotated the same way but a gearbox reversed the rotation of the props.