Sorry you are naive.
You really need to do you home work.
Every, every Australia passenger system, both regional and suburban for the purposes of PT losses money and its not small change. Last I saw the figures its between 65 and 80% depending on the network. That's for every $1 it takes to run the system the taxpayer coffs up up to 80c. The exception is the GSR hotel on wheels, but even the Overland is a money pit. On rail unless you have IP type length trains, moving people at current prices does not pay. The losses in many parts as so bad that increasing services to cater for more people doesn't equal a reduction in subsidy.
Why does the govt do it? cost off-set is a major driver. ie spend less money running a rail line than building a hwy and popularity/public demand.
The ONLY commuter type line that comes close to running at a profit is the Brisbane Airport line. Privately owned, built in 2000 for $220m, for which within a few years the owners/banks wrote off about half as a lost cause and hence the profit margins are now based on the capital repayment of around $110m. And still to achieve this is by charging 2-3 x as much to go to the Airport as it does to go the same distance on govt owned commuter line of similar distance. However note Brisbane which has the highest train fares in Australia (and still needs a 75% subsidy).
So by Mel standards the 15km trip from CBD to the airport at nearly $15 or $28 return is expensive. Tulla is a few km further out than Brisbane airport.
I suspect PPP is what will happen, but I'm sure the govt is worried about the shock factor on fares.