Please, that is not what the government (Australian Minister of Transport) said.
The article meantions the following statement: "
Decisions about when international travel resumes will be made by the Australian Government, ... International borders will be opened when international arrivals do not pose a risk to Australians."
So there was no clear statement that the border won't open by summer 2021. There was just a statement that the government decides based on a risk assessment.
As soon as the government hints a relaxation of rules, you will see QF making new flights availble for booking.