Lawrence is on the right track...
Australia has an enormous agricultural industry, be it the growing of grain such as wheat and barley, or livestock such as lamb and beef.
Back in the 1950's and 60's, when the Australian economy was booming, and our pound (pre-decimal currency) was stronger than the US $ and UK pound, the term was phrased, "Australia was riding on the sheep's back". Wool was our main export item, and continued to be so up until the 1990's.
Given that these are our main industries, and therefore amongst the biggest factors in our economy and gross domestic product, it figures that we will "sell it to the world"
New Zealand is in a similar situation....it seems their entire economy is built on sheep. I can't remember the exact ratio, but the number of sheep in New Zealand outnumber the humans 50 to 1, or something like ridiculous like that. So it follows that they have enormous quantities of lamb that would otherwise rot and go to waste if they didn't export it to other countries.
But I don't think it's a case of "shrewdly dumping dregs". Knowing the stupidity of Australian big business and politics at times, it wouldn't surprise me if Campbelltown was getting the best we have to offer, whilst we here at home are getting the dregs.
(After all, Australia logs some of the last remaining and rarest areas of rainforest we have left, sells the woodchips to Japan, and then buys the paper back from them.)
I suspect the reality is that the Scottish whisky industry is an enormous sponge on local barley supplies, and it wouldn't surprise me to learn that the distillers need more barley than the UK can afford to supply them. So naturally, the Scots look to other suppliers around the world.