Very good summary Madness+ , builders who are serial offenders know that the system is rotten and don't care about defects because they make more money taking on more work instead, and they know they will get away with most of the defects.
Just a couple of points:
It used to be Building Control Commission and then they dropped control from the name and also everything they do. So now there is no control, only the pretence of it.
Building Commission actually has a very powerful tool to use against the builders but it does not use it often enough, or when it seldom does the result is woeful. It can initiate inquiry into builder's conduct with Building Practitioners Board. BPB can reprimand, fine, suspend or cancel builder's registration.
Look at BC prosecutions and the results, it will make you sick.