Something to do with not having historys on them. Probably to do with not knowing how long they had been in captivity, not knowing if any were results of breeding from wild reptiles, not knowing if they might have diseases from the way they were kept and not wanting to introduce possible diseases into the habitat (its a condition of taking these reptiles that you keep the seperated from others in your collection for at least 12 months and that you are to keep them in your possession for at least 6 months)
From the horses mouth Jeff Hardys (From the AustHerps site):
"There is no provenance information so they cannot be released into the wild. They are not required for any licensed exhibit, so rather than
euthanase them, they will be given away by a transparent and
equitable method (by ballot) to interested private keepers."
I have to say that it is a good thing that NPWS are doing. They could easily have sold the reptiles to keepers as other states do. That they just wanted to get them to the keepers asap is a good thing, it shows that they have the reptiles best interests in mind.
It would have been even better if they could have been released back into the wild though