CASA is the airspace and aviation safety regulator. It is they who make the legal determination what level of air traffic service is required in an area or at and in the vicinity of an aerodrome. They do that by conducting aeronautical studies, the outcome of which determines what if any action is required.
Airservices is the civil airspace air traffic service provider, and they provide the services that CASA deem necessary.
Suggest you contact CASA's Office of Airspace Regulation:
[email protected]
https://www.casa.gov.au/airspace/lan...ace-regulation