When the government decided to privatise Telstra, they had two choices: (a) split it up and sell the bits separately, or (b) sell it whole. Option (a) would have maximised competition but reduced the sale price, option (b) means less competition but more one-off revenue for the government. So, which one does the government choose? Option (b), of course!
At the end of the day there was only one set of local loop copper going out to each residence. So no matter how many pieces it had been broken up into, each household was still going to face a monopoly owner of the last mile infrastructure to their residence.
They could have split retail from wholesale. So the wholesale company would have owned the local loop, but consumers couldn't directly buy from them, they'd be able to choose between retail resellers. Which is basically the current NBN model anyway.