Unlimited quota plans are the issue
A 1Gbps connection can consume 324TB of data. Very few people have the need to consume this amount of data, however there are many reasonable examples of ordinary people consuming close to this these speeds (especially above 40Mbps upload) for real-time services (e.g. video conferencing).
If people do not need to pay for something then in general they care less about it. For example how many people would turn off the aircon when leaving for work if electricity wasn't metered?
NBNCo costs are relatively fixed. Revenue is AVC + CVC. If you decrease CVC revenue which NBN has intended from day zero to be the primary source of growth, then AVC has to rise to compensate. If the campaign to lower CVC prices is successful then FTTN is further justified because very few will be able afford truly fast connections.
The simple fact is that CVC pricing effectively causes those people who are placing the most load on the network to pay.