There are a lot of reasons for Australia in particular to take such a prominent role in this trope. It has the qualities already mentioned in the main article, not to mention most of the capital cities are naturally defended by terrain, which is very useful for a supervillain. (Take Melbourne: the only way in by sea, Port Phillip Bay, requires a map or you hit rocks in the shallows; by air you have to travel a few thousand kilometers from anywhere; and by land you have to put up with lots of forests and distant homes.) Plus, they have great beaches.
Add to that the fact that the first British settlements in Australia were penal colonies, and that Australia's greatest national hero was a criminal, and you can see where the Australian people could be inclined to welcome most supervillains with open arms. Funnily enough there are reports stating the Australian army is the second best trained in the world, and there's 75,000 ADF (Australian Defence Force) members to boot. When you factor in that this force reinforces with two additional regiments per turn compared to most other militaries, you begin to see why The Starscream would consider Australia an ideal location to begin pursuing his own agenda.
On the other hand, it's the single most infertile continent save for Antarctica (which, ironically enough, has led to a booming wine industry, since grapevines grow best when made to suffer), precisely because Australia has had little tectonic activity during the past 30 million years, its soils are amongst the oldest in the world, and rainfalls are scarce except in the cyclone-ridden tropical northern parts and in coastal areas, which are subject to heavy floods. Oh, and there are a lot of thunderstorms and lightning note .
In fact the Northern Territory and Western Coast of Australia is one of the most lightning prone areas on Earth. And bushfires. Don't forget the bushfires, especially since they can lead to exploding trees. Eucalyptus trees have very hard wood and highly flammable oil. Add extreme heat to them and they tend to pop like giant popcorn kernels. And spiders so big, they have health bars. In fact, why stop at spiders? A huge percentage of Australian animals are venomous and/or homicidal, and a ridiculously huge percentage of deadly animals are Australian (last count was six of the top ten deadliest of the world). What can I say - it's a land of weird differences - we here enjoy warm Decembers and frigid Augusts. The entire continent can be certifiably considered a deathtrap.
So it's the perfect place to set up a lab if you're a Mad Scientist and need a thunderstorm to zap your Frankenstein's Monster with lightning or to power your flux capacitor. Not so much if your plans include an active volcano Supervillain Lair with Lava Pit. But at least you can get the Shark Pool filled with sharp-toothed predators even on a low budget.