I'm not sure if it has been said yet but the problem was and is that AN (Federal Government owned) let all the branch lines run down by doing little or no maintenance, thereby not maintaining a public-owned facility. So that when the lines and operations were privatised the companies that acquired these assets obtained them in a very poor state of repair.
Because of the neglect primarily by AN (and the legacy of the SAR), GWA in particular would have their work cut out (at great expense) just to run the lines before they'd even turned a wheel let alone generated any income. So while I agree the line to Apamurra is a white elephant it, like the mid north broad gauge lines, didn't have to be. Case in point is the remedial (reconstruction) work currently taking place in the metro area, all because of the legacy of bad management and poor or little maintenance.
The problem as I see it in South Australia (I work in civil design with trains, planes and automobiles) is the lack of planning (foresight?) that goes into anything here. Throw in the NIMBY attitudes, poor cash flow, automatic pollies and the need for federal funding to get any major projects underway kind of puts us in a hole. Obviously the situation is more complex than that (see one Alan Scott, Mt Gambier) and that is why little old SA ties itself in knots. We don’t have the cash to play with so we need to be more careful what we do with it.
A country passenger service to a town of 1,500 when the rail right-of-way, roadside furniture, station and railcar/loco facilities requires a complete rebuild, is just not an option. Now that our country lines are privatised, it never will be because the numbers do not justify it. Our only hope is when the lines revert to state government ownership that the pollies would see sense in say running railcars to Roseworthy, or Mt Barker and so on. The benefits of which are very hard for bean counters to quantify. But that is the point. Build the public service and the public will use it. Metro rail revitalisation anyone? How many people smeg-canned the tram extension through the city at the time? And I use King William St as a thoroughfare all the time (I work in town) without issue. But that was a no-brainer and an easy option. No real opposition there, just public opinion.
I understand the historical reasoning for the existence of some of these lines in the first place (inland connection to sea or river ports, agitation by locals for a railway at the time and hence for political gain) and that a fair majority of the SAR country system should simply have not existed (Cambrai, Truro and Willunga lines to name a few. Although wouldn't it be nice if McLaren Vale was a terminus and the Willunga line still existed to Hallett Cove. I would imagine that hypothetical line would be well patronised.