The main reason why Singapore Flying College (the training arm of Singapore Airlines) is that Perth has reasonably uncongested airspace. We also have a training unit of the Republic of Singapore Air Force based at RAAF Pearce (about 2 kms away from my house) where they use S.211s. We also get the Learjets of Singapore Flying College down here on a regular basis as well.
China Southern is based in Merredin, which is in the wheatbelt a couple of hundred kilometres east of Perth. In Merredin there is NO traffic, so they have the skies to themselves out there.
Cathay would have chosen Adelaide because of their uncongested airspace as well.
Cathay Pacific, Dragonair, South African Airways, China Airlines and China Xinhua Airlines also train at British Aerospace in Adelaide http://www.aac.com.au/
I think that Air Nippon does some jet training (A320s) out of Avalon Airport in Victoria.
So, the answer to your question is that some of our cities have uncongested airspace, when compared to their home countries (i.e. Singapore and Hong Kong), and that our standard of living is high or higher when compared to the home country as well (the standard of living was given as a MAJOR reason when the RSAF moved some jet training to Pearce).