Is the question 'Why are Serbians staying in Australia supporting Serbian team ? '
Good question, I think it varies and depends on a case by case circumstance. I'm not sure who they would support if they were playing Australia. It happens in many sports here and sometimes just for fun.
For example with the cricket when England, NZ, India, Sri Lanka or South Affica tours here you will have some new Aussies supporting their mother team but their kids sometimes will support the Aussies. Don't know about the Serbians.
As a joke the Kiwi's wear this T shirt that says, " I support NZ and every team playing against Australia ".
The Serbian fans are very vocal though and very full on. In the 80's it was the Swedes that had a lot of tennis fans with their painted faces. The English Cricket fans have the "Barmy Army", whereas the Indians have the "Swarmy Army ", fans.