Basically most of their energy is spent on digesting the eucalyptus they eat.
Koalas are marsupials that carry their young, called joeys, in a pouch
The developing joey will nurse inside for about seven months.
Koalas are the sleepiest animals in the world—sleeping up to 22 hours a day
Koalas require a lot of sleep because their food gives them very little energy and eucalyptus requires a lot of energy to digest. Basically most of their energy is spent on digesting the eucalyptus they eat.
Baby koalas eat poop to help transition from drinking milk to eating eucalyptus leaves
The excrement, called pap, comes from their mother and can smell like eucalyptus because of their eucalyptus leaf diet. It has the microbes baby koalas/joeys need to digest eucalyptus leaves.