As far as I know that the State of Victoria ( SE cnr ) has just announced that the season will go ahead this year - Don't know about the other states - I don't Duck Hunt but I thought I'd answer your Q as best I could
Various reasons have been given over the years - Low water reserves ( dry place is Oz in spots) , widespread Drought - (Yep, 8 years of that in some areas/states) Low duck numbers ( due supposedly to previous 2 reasons) and pressure from the anti hunting crowd.............
Read into all of the above " anti hunting minority groups" influencing political agendas using the above reasons to further their cause.
Oddly Queensland ( one of the biggest states is 1/3 under water at the moment with floods ) - guess the "dry" argument won't work in that area for a while.
Down here in Victoria, despite what you may have heard about the bush fires ( 750,000 acres burnt out, 180 dead, 1800 houses burnt out and 7000 homeless - all bad
) it wasn't generally in duck hunting areas and will have little impact on duck hunting.
The Fires have had a HUGE impact on Victoria and Australia in general though