>>1871850In terms of economic reasons, as long as Japan's still RHD, there will be a sufficient supply of RHD vehicles available for HK and Macau.
As for practical reasons, some infrastructure are built with traffic handedness in mind. Trumpet junctions are usually built with the less busy traffic flow going onto the inner loop, as any traffic on that section would be required to slow down.
If the directions were reversed, then the busier traffic flow would be forced to slow down for the loop, while the quieter flow goes on the more direct route.
