In this video How Long Do Koalas Really Sleep In A Day?, it states that
Scientists have long believed that this  may be due to [koala's] position as nature's own teddy bear, but recent studies point to a more biologically sound explanation. The koala subsists strictly on eucalyptus... eucalyptus is highly toxic, low on calories, and very difficult to digest... koalas have developed specialized digestive bacteria that nullifies the venomous effects.
What I only knew is the teddy bear is a stuffed toy. I am not sure how this metaphor is used to explain the Koala's unsmartness.
 this refers to
Koalas are undeniably cute, but they might not be the smartest creatures on the planet.
They chow down on eucalyptus leaves, which are pretty poisonous to most mammals and contain little nutrition.
They look like bears, but they're not bears. Their thumbs are pure body horror.
And they apparently smell about as good as a college roommate who believes that tea tree oil can replace actual showers...
And they sleep a lot. It turns out that the standard koala spends between 18 and 22 hours a day drifting off to dreamland, according to the Australian Koala Foundation.