In the 1980's trains services did operate after midnight in Sydney. However in 1989, the NSW Government made a controversial decision to replace late night rail services with Nightride Buses. It was in response to concerns over violence on trains at night but also to reduce operating costs.
Source: Nicholson, L. "All stations go for travellers: Buses to run taxi service". The Daily Telegraph, May 26, 5.
It was phased in two stages with a trial implemented on the Illawarra, East Hills and Bankstown Lines during June and July. By July, late night rail services on those lines ceased.
Source: Ministry for Transport (NSW). 1989. "Midnight to Dawn Services: Nightride" (Advertisement). The Daily Telegraph, July 21, 19.
Below is a timetable that was published in The St George and Sutherland Shire Leader.
Source: Ministry for Transport (NSW). 1989. "Midnight to Dawn Transport Services: Night-Ride"(Advertisement). The St George and Sutherland Shire Leader, July 25, 30.
Source: . Anonmonyous. 1989. "Night Trains replaced". The St George and Sutherland Shire Leader, June 6, 7.
The opposition were not too impressed. Shadow Transport Minister Brian Langton (ALP, Kogarah) raised concerns that buses would not cope with demand
Source: Philpott, P. 1989. "Nightride bus claim refuted by minister". The St George and Sutherland Shire Leader, July 6, 2.
When initially announced, the reaction from late night commuters was not positive citing that buses added extra travel time, safety concerns and would be forced to travel in taxi's for some or all of their journeys. The article above highlighted a weakness in the Nightride System - Many stations missed out on Nighride services altogether. Note that Penshurst, Mortdale and Gymea have since been added to the Nightride Bus Network.
Those that were happy claimed that they felt safer on buses (research shows that you are less likely to be a victim of crime on a bus than a train).
By the end of the year, it had been introduced on remaining lines.
One advantage of the Nightride Network was the ability for buses to serve suburbs without rail stations including Sylvania and the Parramatta Road corridor. Some suburbs with rail stations ended up having non station stops.
Fast forward three decades later, the Nightride Network has expanded. Services now operate from Town Hall to Richmond (N71) and Carlingford (N61) along with Railway Square to Bondi Junction (N100)