The constitution has special legal status in Australia. Parliament cannot alter it the way they can normal laws. The constitution can only be changed by a referendum - which is vote by the whole nation. What parliament is allowed to do (not Albo individually, but by majority vote in parliament), is make laws under the constitution. So yes, parliament could pass a law that creates a voice. But the next government could then pass a law that cancels the voice. And so on. The idea of putting in the constitution was so that it would have more staying power. If it was in the constitution it could still be removed, but only by another referendum, because as per point A, constitution can only be changed by a referendum.