You're right. The Fitch ferret has been domesticated going back to ancient Egypt. It is a member of the polecat family which includes, weasels, minks, martins, skunks, otters and wolverines.
The wild cousins of ferrets have done a fair bit of raiding around the old hen house, and nobody ever said laws or legislation need to make sense, because they seldom do.
In Georgia's case, in 1977 a pet shop that sold ferrets somehow managed to let a few escape. Several where seen and caught near farms. Farmers not knowing the pedigree of the Fitch got all excited and contacted their legislator and a law was passed making it illegal for pet shops to sell them.
They were legal in Florida, Tennessee, Alabama and both of the Carolinas so it wasn't illegal to buy one in those states and bring them into Georgia, it was just illegal for places like Pet Smart to sell them.
I was able to get with a local representative, and along with a few other people who had a background with ferrets, were able to tweak the law where ferrets can now be sold, but they must be fixed.
This keeps farmers happy knowing the ferrets won't reproduce if they do escape, and more importantly it helps protect female ferrets(female ferrets are called Jills and male ferrets are called Hobbs)A female ferret suffers from a much higher rate of anemia than most other animals.
In order for females to live a long life, they must either breed twice a year or be fixed. If they aren't they have an 80% chance of suffering and dying from anemia than if they were fixed or bred regularly.
Hearing a little ferret scream in pain is very disturbing and not being able to do anything about it is the worst feeling of hopelessness you can feel. I've heard that painful squeal and I don't want to hear it again.
So that is why if you have a female ferret; breed her when she is season or get her fixed.
See!? I told you I knew a tad about ferrets!