'Cause the Army doesn't want one. You should never overlook chauvinism or desire as a motivating factor in defence procurement decisions. A Rooikat would be ideal for Downunder but the RAAC doesn't want it.
Not quite
The main issue for RAAC was finding an AFV or types and numbers to fill the roles.
Under project Waler in the '80s, there was huge debate of wheels vs tracks. It was one of the reasons the project failed.
That and the total lack of experience in building heavy fighting vehicles and an industry to build them (add to tiny run of AFVs with full R&D cost)
The challenge for Australia and defence of the north, half the year is dry with a huge area (wheels!), The other half wet either flooded or dense foliage along the coast (tracks and amphibious!)
Rooikat would be great for dry, but too heavy for the wet. Its 76 APDSFS with 300mm penetration would be good for old T62s.
Throw in MBT for fixed battle at critical points, and the RAAC leopard 1 was not close combat tank. It was designed in the 60's for fast acceleration, thin armour, nth German plain.
Australian leopard 1 only had active IR, basic APDS (no Fin), fixed program computer, night sight only for commander /not gunner and 140mm front armour (70mm@60)!. Side armour is half as thick (45mm turret side) and most autocannon can defeat it with APDS.
Canadian leopards had at least LLTV and APDSFS while in Europe. RCAC was going to replace it with styler MGS. After real combat, that was quickly dropped, Leo 1 uparmoured and then replaced with Leo 2 (800mm vs HEAT!)