Many Australians talented developer and computer engineers have been flocking to USA for mainly two reasons:
1. They are rewarded more in USA, both socially and financially. Who doesn't want to be in the middle of global innovation among other great people?
2. It is much more prestigious and hard to resist. Many US-based companies have been actively recruiting Australians, for example Amazon.com.
This leave Australia with limited local talents and therefore comes up with need to employ overseas eng-IT professionals. Note that 457 are neither cheap nor simple to lodge and employ. We are currently at a phase where it is necessary to keep feeding our demand of technical professionals to keep the growth of Australia tech industry.
That's the reason you post it here anyway.