The 457 visa was a government program that was being exploited, and quite obviously too, for quite some time, just like any government program eventually will be. For another recent example, look at what happened to the child care subsidy program. Government programs can serve a good purpose if they are well regulated and audited but comically and sadly for citizens they never are.
I just wonder if the 457 reforms would have taken so long if the Commonwealth Public Service had outsourced their IT to some South Asian consultancy and discovered that suddenly and mysteriously there were not enough skilled Australian IT workers to support them in Canberra (and elsewhere) and rather rapidly offices were filled with 457s. But this is exactly what large corporations in the private sector have done.
In IT and other sectors (notably health), companies are using 457s to save on employee salaries, pure and and simple. I have knowledge of assistants in medical practices being told to accept the lower salaries that their 457 co-workers are on or lose their jobs.
Oh, and it really annoys me what Atlassian founder Mike Cannon-Brookes keeps on saying. How about you invest in training locals instead of whinging all the time about not being able to import people?
BTW, I'm a UNSW CompSci graduate, 40+, have a lot of international experience, can operate at the technical and business level, speak a couple of languages, and after my last (5-year) contract ended I spent 2+ fruitless years searching for more IT work, while conspicuously the suburb I used to work in (with telcos, Cisco and software companies) filled with people from certain demographics. Despite all my experience, I didn't get invited to a single interview. Not one. Ageism and 457s killed the job market for people like me.