To be fair, real life Koalas are easily one of the dumbest animals going, with the actual smoothest brain of any mammal.
And the reason for that is their primary food source, Eucalyptus leaves, are so nutritionally poor that they're can't afford the extra neurons.
Hell, they're so built on instinct that they'll only recognise Eucalyptus leaves if attached to branches.
So if any mammal was going to be depicted as non-anthro, they're a pretty good candidate for it.