Surely a 737 would be able to divert somewhere closer than Melbourne?
Canberra? Williamtown / Newcastle? Even Richmond comes to mind.
Can one get a clearance into Richmond at very short notice late at night?
If one lobs into Richmond or Willy are there steps? Where are the pax going to be put up? Are there staff there to meet 'n greet the pax and/or aeroplane. I
suspect MEL was a much easier logistical answer.