In theory it is true that people can return, but practically that is not true - and there are many horror stories to show for this.
If you have no bumps in the road however, then, as you said, the cost of travel and HQ is simply prohibitive for some - this cost alone is $7k as a minimum and rising from there.
But there are other costs that people in Australia can't seem to understand, so let me highlight them. Many people have had their flights moved, or cancelled, and that means they need to spend more time at their origin. When someone has finalised their rent for example, and they then face a delay of one, two, three or sometimes even more delay - where are they going to stay? And because they're not renting, this often means a hotel or Airbnb at short notice. If it was just two weeks delay, this can mean anywhere from an extra $1,500 to $3,000. Europe and the UK are extremely expensive when it comes to accommodation.
I haven't even mentioned the fact that two weeks confined in a room is two weeks of time lost, no matter how you spin it. Not to mention the mental and health effects of being in a room for 14 days.
As I said before, if there can be something done for 1200 foreigners for a tennis tournament, I don't think anyone seriously can say we can't do something for fellow Australians in need. That is simply ridiculous. I'm not saying, nor have I ever said just open the borders freely, but there are other ways. One of the ways we can start to ease borders is the vaccination program. Yet, no one seems to care.