Revealing mistake: When Nullah and his mother are being pulled out of the tank, the stitching on the dummy used for the mother is visible.
Revealing mistake: When Fletcher is killed by King George, the spear can be seen as computer-generated; Fletcher swings his arm back and forth, through the spear. At one point, he even pauses, with the spear in his arm.
Revealing mistake: When Lady Ashley tells Drover not to bother returning, tracks made by very wide tires are visible in the road as he rides off. Vehicles of that era had very skinny tires, so the tracks are likely from the filmmaking crew.
Answer: So they'd be unable to water their cattle. Which has two benefits for Fletcher. The first being that they'd have to take their cattle to the watering hole on the border of their property, making it easier for Fletcher to steal the cows. Second, and more long term, their cattle would be of poorer quality due to lack of proper care. The ranch would lose money as a result, and they'd be more amenable to selling the ranch to their competition, whom Fletcher works for.
Phixius ★