The geography of Melbourne is different to Sydney. Melbourne CBD is centralised. Sydney CBD is in the far east of the metropolitan.
Most Melbourne AFL clubs existed in 1897 and are based closed to the CBD. Even the ones admitted later like Hawthorn, North & Footscray that came in the 1920s were already set up in a different comp and are relatively close to the CBD.
Sydney clubs are younger and set up in metropolitan regions outside the inner city where there was population growth. St George in Southern Sydney 1921, Canterbury in the Canterbury-Bankstown district 1935, Parra & Manly in the Hills District and Northern Beaches respectively 1947, Cronulla & Penrith in the Shire and outer Western Suburbs respectively in 1967. The only inner city clubs that remain in the NRL are Roosters and Rabbitohs. Those two clubs have supporter base similar to Melbourne AFL clubs, they come from all over the Sydney metropolitan, particularly Souths.