Yes there's the question YM-Mundrabilla and not new I think.
After how many years, was it 19 that I read, this Cement Bulk service has been operating this way, surely someone sometime would have raised it before this occurrence?
I would suggest the economics of this train's operation was set 19 years ago and perhaps it seems, there hasn't been a provocation to test the original measures of containment - until now. More likely that the old electro mechanical / pneumatic locomotives had reliability of function and resilience to the locomotive environment compared to the low sensitivity a microprocessor based systems and so there's probably not been any issues with the locomotives brake systems with the old locos
In trains that are directed to operate this way, the Driver on the train is just a different safeguard to another. The risk protection factors level out fairly early in the calculation of protection levels with the implementation of a few independent redundant safety measures in place, usually cheaper to add simplistic safety systems than human management.
And significantly, the expectation of a human correction to an on board failure is fraught with other variances just like what has happened up in the north west of Australia.
Broad systematic common failure from place to place can be undiagnosed or unrecognised due to "administrative policy" or is it "policy administration" until a serious issue has taken place.