Because the RSL (Returned and Services League, Australia's major body for veterans) doesn't support the idea.
How would you create such a thing? Would you dig up bodies that are typically buried either in Commonwealth War Cemeteries around the world near where they fell, or which were returned to Australia and buried in their local communities near where they grew up and where their families were?
Arlington is a sacred place and a wonderful tribute to America's war dead and her veterans - but it's an American tradition. For us, our tradition is to bury our dead near where they fell, or where it is possible to repatriate bodies (as nowadays it is) to bury them where they grew up.
For us, the great places of pilgrimage and tribute are our War Memorials and Shrines.
From the grand structures of our major cities:
to the tiny memorials in every little town and suburb:
LET ALL MEN KNOW THAT THIS IS HOLY GROUND. THIS SHRINE ESTABLISHED IN THE HEARTS OF MEN AS ON THE SOLID EARTH COMMEMORATES A PEOPLES FORTITUDE AND SACRIFICE. YE THEREFORE THAT COME AFTER GIVE REMEMBRANCE.
We have the memorials we want and need. Our fallen rest where they grew up, or if its overseas, it's in a corner of a foreign field that is, forever, Australian.
Efforts are being made to ensure that every veteran or fallen soldier in an Australian cemetery has an appropriate gravestone that acknowledges their service, with repairs being made where necessary and new plaques installed where needed:
I think most Australians would say that, for us, this is the way to do things. It's our tradition.