Three reasons:
1. The quality of batting is poor
2. There are stacks of good pace bowlers around
3. Those pacemen are quite often benefiting from very helpful pitches
Not sure how the quality of batting is poor because there are atleast two or three pretty good batsmen in every side, who if nothing else should ensure that their teams don't cave in as badly as they are doing atm. Also the number of runs being made by the lower order batsmen from every side is another indication of how hard/unplayable the conditions are, especially when the ball is new and has a profound seam.
I agree there are a good number of fast bowlers around, but out of them most are either injured or on national duty, Harris, Hilfenhaus, Faulkner, Hazelwood and Coulter-Nile are possibly the only bowlers currently involved in Shield cricket who one can tag as international quality fast bowlers, but funny thing is its guys like Butterworth,Hastings, Sayers, Hopes, Sandhu, Sheridan and Putland who are taking most of the wickets, in fact it almost seems as if you bowl military meds then all you gotta do is roll your arm over and you would get a few wickets.
These sort of conditions are obviously diluting the standard of first class cricket in Australia, the structure of 6 state teams and 66 of the best cricketers in Australia going against each other was a great strength of our team, but that same strength has now become a weakness because a lot of players in the current Shield sides are either well below international standard and the good one's are getting handicapped by the conditions.
Australian cricket's general strengths over the years have been in producing fast bowlers who hit the deck hard at good speeds, batsmen who are good at playing the horizontal bat shots and hitting through the line of the ball and producing good quality wrist spinners, possibilities of producing those type of players is highly nullified in the present set of first class conditions and this is the root cause of most of Australian cricket' current problems.