Most of the exports occurred at a time when our population was relatively healthy. Taronga had three breeding females and Melbourne had five females. Since then, the females have all become reproductively unviable due to age, death and social issues and new females are needed.
All of the females were all around the same age too, so by the time they got older and become unreproductive for varius reasons, we had no viable females left as all had been exported overseas. Poor planning at it's best.