They had full VOR and ILS capability and could easily have flown the approach back to Sydney. I guess not having a magenta line scared them.
Sydney now has no VOR. Also, the magnetic heading data fed into the VOR systems is based on IRU present position (which appears to have been wrong). I'm surprised the aircraft reached Melbourne with vectors (unless they were using their whiskey compass).
Turning off intertial reference systems at the wrong time hasn't only happened to budget airlines.