They do… 1/3rd of it is used that way.

There is a bit of a scandal in aus at the moment about this. Qatar asked for more international flights (they back Virgin Australia, one of 2 major domestic carriers in Australia). Government said no, for undisclosed reasons.

The “national” carrier Qantas are scumbags with the government in their pocket and likely quietly lobbied against it, but also Qatar International Airport did this to Australian citizens not that long ago:

https://amp.abc.net.au/article/12817070

So it’s just kind of dickheads all the way down.