Your government may not need additional taxes so they prefer not to tax its people because the Australian economy is robust, but other countries are not that robust they need additional funding so instead of resorting to borrowing from local and international banks they prefer to tax the gambling sector.
I have seen how taxing the gambling sectors can do to one's economy because I'm living in a country where so many things are being taxed, and gambling is one of these.
Our country takes 20% of the cut in the winners' winning besides different taxes within the gambling sector, our government is good at collecting these taxes.
Damn, is your country the same as mine?
Recently, a country very famous for its high taxes (brazil), the discussion about means of applying taxes has been increasingly frequent, even talking about 'sin tax' for games of chance, with the excuse of discouraging gambling sector. But they will continue to collect, the government doesn't care about collective health, so this is just an excuse for them to give the population to justify this high tax rate.