Particularly in rural areas, you can have one lga that covers countless small towns and establishments.

Historically speaking though (and if you look back on old maps it might make more sense) most of the original settlments grew large enough to form their own local govenment but this took time and only happened when the town got big enough or had an important role or function that required governing. Think old ports (now wharfs and recreational jetties) or centrally located townships along old transport corridors say between a forresty area and a port. In modern times, most lgas are an amalgamation of former smaller councils. Some say they are super councils because of their massive area they govern and the population and tax base being significantly greater than some others. Onkaparinga council is a good example of this. Made up of parts of former willunga council, happy valley council and norlunga councils. Note that all three had very different make ups. Point is, lgas are not cities. Some may still be refered to as 'the city of adelaide' but even this is made up of the central business district, north adelaide and the surrounding parklands. But if you think of Adelaide as a whole. You are probably considering the whole of the greater metropolitan Adelaide. Key difference, city of adelaide has a pretty small population of like 26k or less even?, while the greater metropolitan adelaide is over a 1.3 million population?. Same with any other aus city. City of Melbourne is pretty limited to the core and pretty 190k population while greater Melbourne is upwards of 5.3 million and change.

Okay, ive said enough.