How do the reproductive habits of koalas affect their genetic diversity?

Koalas, scientifically known as Phascolarctos cinereus. They found in the variety of habitats such as coastal islands and eucalyptus forest. They live in societies and rely on genetic diversity for survival like any other species. But in case of Koalas, the genetic diversity low over 120 years. Low diversity indicates that they practice inbreeding for reproduction. As a result the population size decreases.