You could even take this argument further and ask why there is not at least one CATII/III approach into Mel
Reading a current APAM (Airports Aus, MEL) publication today it states that "later this year the airport will be capable of CAT IIIB approaches".
The article revolved more around ground surveillance radar for vehicles operating on taxiways and runways having transponder equipment fitted for low vis ops.
A quick search of the APAM website revealed no info though.