SAP was determined by the contractors who scoped the replacement
SAP was predetermined by the contractors who scoped the replacement system two years ago. All they did was rock up and proceeded to sell it to the DHS SES. It is supposed to replace the Model 204 based Centrelink system as well as the IBM mainframe based Child Support System. It has been touted as the answer to all things. They truly believe they will be able to wrangle it into a complex case management system (think managing and investigating child support non-payers as well as Centrelink fraud), client contact system and ultrareliable daily payment system all at once.
Needless to say they drank from the corporate trough muchly and will believe anything consultants say when they are paying them lots of money. Personally they requirements are so specific they would be better to design and build the system in-house but that is totally at odds with the current public service ideology.