It is illegal to keep a koala as a pet.
Koalas are wild animals. They are specially adapted to live high in the treetops, and they live quite alone.
For these two reasons alone they do not make good pets, because they would not be able to live the way they are made to live.
Even hand raised joeys that live in zoos would run straight up a tree and never come back if they got out. This tells us that they might be healthy and seem ok, but if they had a choice they would never come back.
Koalas look very cuddly, but they don’t like being handled and have very long sharp claws and teeth. If you ever see a koala, even if it looks quiet, do not attempt to pick it up.