One possible explanation is that they can occur in made up ground. In time the fill compacts leaving a void and when the earth above becomes too saturated to support itself it collapses. There must be a void for a sink hole to occur.
Well, if the Aussie authorities didn't get you The Nothing would, and, as Ped explained, you would be sucked into the void. If you were to run it would become a never ending story of trying to avoid the void.