Maybe they haven't got the right people to generate suitable reports. Anyone can get out and kick around busted up tin and map an accident site with a bit of training, however to to follow through with a full in-depth and and accurate unbiased technical report can be a challenge for your average subject expert, ie pilot, engineer, air traffic controller, etc, if they haven't done any report writing in the past.
No just any pilot or engineer can just walk in the ATSB's front door and start generating suitable reports, it takes years of experience - even for highly experienced pilots and engineers.