A heavy maintenance facility has to be set-up for a specific aircraft type with lots of specialized tooling, equipment and personell. The only way for a facility like this to be economically viable would be if it is in constant use. Qantas do not have enough A380s to keep such a facility in constant use.
It is a similar story with the Qantas 747s, they used to operate their own heavy maintenance facility in Avalon, Victoria. Once the 747 fleet was reduced below a certain number, that facility was no longer viable.