Melbourne’s airport is very annoying when compared to Sydney. To get to the CBD you have to go and stand outside to wait for a bus that comes every ~15 minutes and takes half an hour to get there (or pay an exorbitant price for a taxi or Uber), whereas in Sydney you’ve got a direct train that gets to the city in 15 minutes.
It's been a while since I caught the train to or from Sydney airport but, in true Sydney fashion, it's privatised and costs an absolute fortune. From memory it costs more than Melbourne's SkyBus.