IDK, at a guess it would have been for two reasons. First and probably the most important was that it looks like the Ecotec was never used in any AWD/4WD application in anything else, so no off the shelf AWD gearbox or engine management (or if they did in the states it would have almost certainly been transversely mounted). The functionality of the Ecotec ECUs are largely unchanged from the introduction of the Ecotec (and even then they seem to share a lot of similarities with the VN-VR ECUs). This would have meant that Holden would have had to develop the AWD capability for the engine/ECU on their own or adapt other ECUs to an existing model in the middle of production. Looks like the HFV6 was developed with this in mind, it's in a bunch of AWD stuff that mounts it longitudinaly. Second reason after taking the first into account, they were gonna ditch the Ecotec in the next series so why sink all that money into the dev for just the VY, particularly as the Adventra was introduced a full year after VY production started.
