Regulatory Capture.
The government didn’t want to be in charge of this, so they’ve offloaded the responsibility (and the power) to a private organisation, in this case the Game Management Authority.
The GMA aren’t all bad, they are also a primary driver behind the protection of native waterways (that just coincidentally happen to be duck shooting spots).
As a shooter, I have complex opinions about groups like the GMA and SSAA that theoretically exist for my benefit.
There’s venison farms.
I don’t know how many or where.
Theoretically all the ferals are escapees, as they have never been officially released (unlike rabbits, foxes, cane toads etc).