Why couldn't the Bureau predict what private forecasters could?

More than two hours before an "inland tsunami" smashed into Grantham, private weather forecaster Anthony Cornelius posted this warning on Weatherzone:

Concerning for the Gatton-Grantham area right now with very large storm/rain area moving towards it with no doubt, torrential rainfall...I hope they're prepared for it, but sadly I think most won't know until the water starts lapping up at their homes due to our insufficient warning system.

Only four hours later, after Grantham had been submerged and lives lost, did the Bureau of Meteorology issue its own warning.

I repeat: we need to know if more could have been done to prevent this tragedy.

(Thanks to reader Glenis.)