They only have home brands, and seem to be a lower quality than Coles and Woolworths. There is also the matter of having to wait in line at stores where they don't have self-serve.
Finally, someone speaks the truth. Would you start a business making so little profit? If you shop at Aldi, all the profits go overseas to Germany. They also don't need to declare their profits, so they could be making more than Coles or Woolworths.