Something Bad may or may not happen to Australian CNI by way of cyber attack in, say, the next three years. The probability of that is unknowable.
ASC have made an (educated) guess that it won't.
If they're right, they won't get any thanks for it. No-one's going to be asking questions in Parliament congratulating them on their prescience.
If they're wrong, they're going to be dragged through the streets behind the metaphorical technical of public and political opprobrium.
Thus, this tactic is one that can only lead to a draw, or a loss.
If they'd said "Arooga arooga, the cybers are coming" and nothing happens, no-one will blame them, because the need to improve security is universal; any improvements can only be beneficial, and have a mitigating effect on the overall, aggregate cost of Teh Cybers across the entire economy.
If they'd said "aroooga!" and something /does/ happen, they will get to look good, *and* be able to shift the blame onto those organisations who tuned out their comms as just more noise. "We warned you!"
win / win.
And that, O best beloved, is why the founders of cyber security firms in California all drive Porsches.