From a story on futurity.org headlined “Why Australia Has Lots of Kangaroos But No Tigers”:

A new model clarifies why millions of years ago more animal species from Asia made the leap to the Australian continent than vice versa.

The climate in which the species evolved played an important role, researchers report.

If you travel to Bali, you won’t see a cockatoo, but if you go to the neighboring island of Lombok, you will. The situation is similar with marsupials: Australia is home to numerous marsupial species, such as the kangaroo and the koala. The further west you go, the sparser they become.