It did not find that it was wrong to pay for the memberships because the rules did not forbid it. Almost all parties around Australia condone the buying of memberships. The courts may supervise the rules of the parties and ensure that they have proper dispute and appeal processes, they cannot establish rules for the parties. Therein lie two problems. Some party rules are inadequate, and enforcement of the current rules is sometimes inadequate.
Parties have a virtual monopoly over the election of members of parliament.
They are the gatekeepers. They could reprivatise, go back to traditional sources of funding and support, and remain master of their own destinies, or they could acknowledge that they are public property and run their organisations according to public rules. They must ensure the integrity of their membership and processes. If they don't, then someone will do it for them.