Comparing now with the old pre-"reform" days, there's a lot of costs in the industry which simply didn't exist at all in the past.
Wholesale market price risk. No such concept previously but now it's a very real thing and a "risk premium" tends to be attached to a market that can rise 35,000% and then crash 99% in less than a day.
Retail cost is another big one. Used to be very cheap to just send out the bills and take payment but now it's $ hundreds per year for each household. It's a cost comparable, in some cases larger, to that of the fuel going into power stations.
All those regulations and regulators don't come cheap either and nor do the assortment of non-engineering focused things they come up with. Ultimately that's how networks ended up costing a fortune.
Then there's the underlying motive of the industry and this is a very key point. Today we have numerous companies all with their own set of overheads and all seeking to make a profit.
Now go back 25 or more years and read the annual report of any of the fully integrated state electricity authorities. SECWA, ETSA, SECV, HEC and PAWA were all the same. In the report you'll find a description of what they were up to at all stages of the industry from generation to retailing but there's one theme that was incredibly consistent year after year and that was
cost minimisation.
All of them could and did supply power, that was a given, so to the extent that there was something to be achieved it was to drive down costs. The SECV and HEC were the ones vying for top spot in that game, and in different ways both achieved it, whilst the others were also incredibly focused but had the natural disadvantages of higher cost available resources although their achievements were still impressive by any international mesure.
That competition was pretty intense at times since they all saw that broader economic development was an unstated part of their mandate. Driving down costs was the key to making that work so that's what they did.
That model gave Australia as a whole the third cheapest electricity in the OECD, beaten only by Canada and NZ with their large hydro resources. From an environmental perspective it's worth noting that we also had the most energy efficient fleet of fossil fuel power stations anywhere, Australia was No.1 in that regard.
I left Qld and NSW out of that list because they had a different model with generation being separate from the distribution and retail side. It worked just as well both physically and in achieving cost minimisation but turned out to be more prone to political interference in practice.
Not a lot more can be said really. No amount of economic theory will change the reality that from the perspective of consumers the present system is far less efficient (both economically and technically) than what it replaced.