Because demand for coal and steel (our main exports) has weakened. People trade currencies in order to buy commodities in that currency - eg you buy USD in order to buy goods from the US. Hence, simple demand/supply dictates that if demand for Australian goods goes down, so does demand for our currency, and hence the value of the dollar drops.
Just quietly, I doubt if we'll see the Aussie buying 0.95USD again for a while...
And as for the sellers - maybe some are profiting by claiming the dollar has gone down when they're selling stock they bought months ago with a better dollar. However, if they bought that stock recently, then massive price hikes aren't actually unreasonable given that the currency has dropped ~30% in value...
That's my 2c... er.. 1c
