The purpose of the Treasury costings is so that we, the voters, have the best possible independent information available to make an informed decision on who to vote for. You should know this as it was the LNP who instigated the policy.
LAB's policies were costed by Treasury. LNP's were not (until forced to by the indies (bless their souls)). Good for goose good for gander.
When LNP provide a cost benefit analysis on their baby leave crock scheme, LAB should do the same with NBN. Good for goose good for gander.