Ultimately the power grid is one single system serving everyone and by virtue of its operation redistributes the efficiencies gained by doing so. That doesn't mean it can't be a capitalist for-profit business, but it does have an inherent dash of socialism embedded into the very nature of it as a shared system for mutual benefit.
In practical terms if we consider a small consumer, eg a single person living by themselves in a small apartment, right up to the largest consumer on the grid (which for the record is Rio Tinto) then both benefit from each others' existence. The economies of scale and improved system load factor brought about by RT's operations benefit the residential user in their apartment. The existence of the small users taken collectively lowers the cost of supply to RT. In other words, everyone wins.
Hence the mining companies where they run generation have never objected to the idea of providing bulk supply for someone to distribute to others.
If you go to Mt Isa well there's one system that serves everyone - mostly mining but households are also supplied from the same source.
Go to north-west WA and ultimately it's big business generating and using most of the electricity, the transmission is mostly owned by mining companies, but Horizon Power, a WA government entity which supplies small consumers, is ultimately just distributing bulk supply obtained from the same system that primarily exists to power the mines.
Once people start thinking individually, that's the surest way to increase costs. Because the key to keeping costs low is firstly scale and secondly it's the benefit of diversity of demand.
Regarding the latter point, in short not everyone will have their individual maximum demand at the same time and that being so, if we put everyone on the same system then the generating capacity required is very much lower than would be required if everyone ran their own separate system. That's a big part of the reason to want the system (grid) to be as large as possible.
For a somewhat extreme example of that, peak demand in Queensland is a full 6 months out of sync with peak demand in Tasmania. Hydro inflows in north Qld are also very much out of sync with those in the Snowy, Victoria and Tasmania. That being so, there's fundamental logic in having them interconnected, it enables the system to work with significantly less capacity than would otherwise be required.
Another is that SA and NSW peak doesn't occur at the same time. Can occur in the same week but it doesn't occur at the exact same time, so interconnection does enable some sharing of generation and reduction in cost.
Once it goes down the track of individualism, here comes a price rise for everyone that's a given. That's partly where it's going wrong, ideology hell bent on doing things that increase costs.