You know my cynical side is saying that they're protecting themselves from future abuse claims; 'I was abused in scripture class'. That's the only incentive I can think of for them.
Possibly, but I think there's a simpler explanation -- they just can't be bothered!
From what I recall of conversations with Service Department about this some years ago, there was a recognition that BOE were rather lethargic about getting scripture teachers assoigned. More than that, BOE were tardy at even promoting it. My gut feeling is that the Branch came to the conclusion that it wasn't worth the effort.
Then we know that they would also have confronted the issue of child protection. All persons in Australia having any contact with children in their work, both paid and unpaid, must comply with the Child Protection Act. This means that scripture teachers would have to undergo special training and to comply would have to attend a course. Other churches have written their courses and have trained their people but who in the Australia Branch could be bothered writing such a course? Just too hard for them!
In the church I attend, there was no shortage of enthusiastic volunteers to be trained - we have a around 3 dozen people trained now, including people who teach scripture, people who mind kinds at creche and so on. Makes you wonder why those "Babylon the Great" people have more of a heart for the children's coming to know God than the Australian dubs do, eh?