Your delightful scenic tour of Sydney and its environs was courtesy of the local politicians. The areas under the runways at Sydney experience a little aircraft noise (nothing like the amount there was even 20 years ago!) and, after buying their houses complained to the politicians.
In a typical bit of politician logic, the politicians around Sydney promised to force the Civil Aviation Safety Authority to change the flight paths around the airport to "share the noise" between the "poor" areas (the houses with the high noise) and the "rich" areas (the houses in areas away from the flight paths).
This of course ignores the simple truth that it was NOT a decision to fly aircraft over poor areas - it is because those areas have some noise that the housing is cheap, and so poorer people can afford to live there!
In order to "share the noise", it is simply not possible to reduce the amount of noise in the busy areas (or the industry would simply do it anyway) - so we now have a procedure where we are
forced to descend to low level, and fly around the city over the normally quiet areas so that they experience some of the noise which the necessarily noisy areas have. 
Sydney noise sharing policy
