I think the specific case of Australia can be explained like this: If, for example, an arbitrary country in Europe (EU or non-EU) would do things like this, people would consider moving to another country. There would be pressure from neighboring countries, since inter-country trade and commuters would be affected. (Also, the whole EU thing makes it harder for any one country to change too much.)

Australia, on the other hand, can do whatever they feel like, and people who live there have no real recourse. They have, if you will, a monopoly on government.