For me CTA access isn't about landing at Class C & D airports, (why would I want to go to Moorabbin, Essendon or Bankstown etc)
It's about being able to transit the airspace.
ie
East Sale
Coffs Harbour
Sydney Basin
Greater Adelaide.
and i'm sure there are others.
These are all significant road blocks and the alternative routes either put you down really low, over tiger country or over deep water offshore, all of which create greater risk. Sometimes the alternative is to track significantly longer distances to avoid them all together.