Because Australia's pace attack can blast them out on a placid pitch. Their Anderson-less pace attack can't do the same.
It's a bit of dilemma for them, they could only win on a ridiculously doctored pitch to favour their seamers and then hope they bowled first.
The Australian middle order unfortunately continues to collapse. I don't know what they will do with Clarke, can't axe the captain halfway through a series but that's the price the selectors pay for picking a bit of a Dad's Army on a farewell superannuation tour. Might have got away with it in Oz.