But that is precisely what Australia are doing for most of the other countries! If South Africa or India someone else were to call Australia for a tour in their winter, Australia would refuse because that would collide with their preferred season.
The reason for this probably that teams can't come here in March/April because that's when the AFL season starts and they need the G. If we didn't have the G and the SCG during those times, we'd be playing on grounds that had less than 5000 seats!