The constitution is not to be trifled with. Section 128 is designed to ensure that it cannot be changed at whim. In the words of Quick and Garran:

These safeguards [e.g., the double majority] have been provided, not in order to prevent or indefinitely, resist change in any direction, but in order to prevent change being made in haste or by stealth, to encourage public discussion, and to delay change, until there is strong evidence that it is desirable, irresistible, and inevitable.