Why is Australia mostly unpopulated

Is it uninhabitable?

it is inhabitable around edges and across entire country by those whom know who to survive. its past history allowed it to go virtually unnoticed by rest of world until it was 'discovered'.
its local inhabitants had to survive by hard won lessons on bush craft etc so natural environment and poisonous snakes etc killed or kept local population to a small level.
hard to find enough food even with bushcraft for a large party of people but small groups manage to survive easily enough on the often meagre food sources available plus fresh water etc.
it was only in recent history that Australia effectively like america has been swamped with immigrants. funnily enough other countries such as Uk are also being over run with immigrants changing ist culture etc out of all recognition form just a few decades ago.
so its really simply due to its harsh environment and huge landscape with limited food resources.

Also their immigration laws are much stricter than ours: they don't let in every Tom, Dick and Chavvy. Seriously though - the other poster was correct, the outback is a desert. The only people who seem to survive in those conditions are the native Aborigines. Then again, they have been living there for centuries, long before it was populated by immigrants. My cousin has lived there for 40 years and even he was a dipstick and broke down in the outback, not realising it is akin to the Sahara desert. Only out there for 1 day, and nearly died, had he not been rescued. Australia had camels shipped from Egypt many years ago because obviously they can survive desert conditions. Oz now has a bigger camel population than the middle east - apparently they are overrun with them.

Australia is sparley populated through out the interior Australia has scarcely more than two persons per square kilometre of total land area, this raw figure is highly misleading: most of the continent is desert or semi-desert and of limited agricultural value all of the vast deserted areas are habitable but is not in the sense of wanting to live in the desert so most stay where water is available

I heard it said that Oz is like an old woman's fanny, everyone knows where it is, and what it's used for, but no-one wants to go there.

Because the Australian Government are clever and doing what UK should be doing and not letting all and sundry cross their borders,they actually kick out illegals a.s.a.p

There is a lot of desert there and it also can get very hot in Australia.

Large parts are desert, especially in the center.

Because of the deserts and kangaroos. i heard their vicious