The reason for that actually makes sense. It’s rarely clear how and when someone contracted a prion disease at time of diagnosis, and often it is unclear which specific prion disease a person has. While it may seem that a father contracted a prion disease after you were born, it could also be that the father has an inheritable prion disease that you too may have inherited.
Not a good comparison. To produce milk regularly cows must give birth. These calves are often sold to be slaughtered as veal. Likewise situation for eggs. To produce hens farmers typically wait until the chicks hatch and throw the unwanted male chicks in a grinder.