There are several reasons why the name "South Australia" was chosen over "Southern Australia". First, the name "South Australia" is more concise and easier to say. Second, the name "South Australia" is more specific, as it indicates the exact location of the colony within Australia. Third, the name "South Australia" is more distinctive, as it helps to differentiate the colony from other parts of Australia.
Over time, the name "South Australia" has become synonymous with the state of South Australia. The name is used to refer to the state's geography, its history, its culture, and its people. The name "South Australia" is a source of pride for the people of the state, and it is a symbol of their unique identity.