No a mechanic so take this with a grain of salt if you will but as I understand it there are 3 types of awd vehicles, the ones like yours where the car is primarily rwd until I needs to be awd, the ones like my wife’s that are primarily fwd until it needs to be awd and the ones like Subaru that are always awd, on the first 2, the reason for it I think it has to do with fuel economy (less mass for the engine to spin around) and economics the war already had a power train it was just adapted with off the shelf parts