Nicely said Andy, they all just want to complete jobs as quickly as possible. In new NBN roll-out areas they just do the straightforward installs. Any difficulty and the house gets skipped.
As an example, we don't have NBN but the house behind us does. In a 4-townhouse block next to us the first and the fourth townhouse are connected to NBN but two middle ones are not. On the other side similar story, the front unit is connected but the back is not.
And to make things worse, 8 months ago when they were laying fiber optic cables they did something and basically halved our ADSL speeds
So no surprise about the dodgy installs