Is there a gate on the two individual driveways? Do all the gates (or just the central gate if that is all there is) restrict access to the common property and thereby increase the security of the common property?
If security is increased by restricting access to the common property, then there is a benefit to all and the cost should be shared by all.
If there are security gates on the individual driveways as well and those are common property, then it makes sense for the whole OC to maintain all three gates. The alternative would be for two owners to be fully responsible for one gate each. Even if the owners with individual drives do not care to use the common property behind the central gate, I presume they could if they (or another owner of their unit) wanted to. In that case, they also gain a (potential) benefit from the gate and should pay their share.
I would expect (from another jurisdiction, not Victoria) that the OC generally pays for common property stuff. Where I am some units have their private driveways directly off the public road whereas other units connect to sections of road on common property. Maintenance of the sections of road on common property was always an OC cost, even though a subset of owners might only walk on it sometimes but are unlikely to have a reason to drive that way.