Correct, in Australia .com.au is popular.
Today, there are 2,645,565 .au domains registered, which isn't too bad for a nation of 23M inhabitants. The TLD is restricted.
Some Australian end users may be interested in the .com of their .com.au, especially if they do business internationally.
But since brisbanefarmers.com.au is not taken the .com must not be valuable.
Do farmers purchase domains often ? Cooperatives might but not sure there is a lot of buyers.
In many Western countries the local extensions (ccTLDs) are dominant, many domains are registered by end users in the local TLD and they're not even interested in the .com. This is a trend in countries that have strong ccTLDs.