You keep ignoring my point but let's try it with a concrete example:

Sydney-Newcastle: ~190 km project length, incl. 70-155 km tunnels, covering both sides of the urban Sydney area, all underground.

So this project would include one of the most central and also challenging parts of a potential HSR network. Cost estimates are somewhat elusive but I found talk of 90 bn AUD. Now, there is a lot to unpack there.

First of all, when we compare that to the current project Lyon-Torino, technically not HSR but still designed for 220 km/h, comparable to the tunnel section in the Sydney-Newcastle plan. It comes also with 100 km tunnel (much of it an actual base tunnel) and 170 km of non-tunnel parts. Price tag: 11 bn EUR ~ 17 bn AUD. Or let's look at the 55 km Brenner base tunnel, designed for 250 km/h, one of the longest base tunnels involving very tricky geology. Price tag is similar 8-10 bn EUR. So even if we compare the rough Sydney-Newcastle plan with very expensive and challenging cross-border rail projects, across the Alps, in other high income, high regulation countries, we are talking about multifold higher per km prices. How come? Likely for similar reasons as in the US or Canada, political and legal reasons. At least in the US, the overhead of any rail infrastructure project is enormous and overshadows the actual construction costs. Extreme bureaucracy, very pro-nimbyism laws and the requirement of minimal or even no negative impact on car traffic during construction. This can be seen when we are looking on the tunnel length in the Sydney-Newcastle corridor. What is commonly reported is on the very upper end of tunnel usage. There is a reason for that and that is also political and legal. While highways were bulldozed through urban areas, rail projects are are rather pushed underground on the entire length, not even using any existing corridor on any of it, until the very end of suburbia and even then. Now, one can debate of course pros and cons of that. There are good arguments for the tunnels, also for speed and operation but it adds a lot of cost. However, even if we don't debate the tunnel length, the costs are astronomically high in comparison to projects in other high income countries, that are not part of the English speaking world.

PS: Even though your own video pretty much is all about the lack of political will and the requirement of it to be at least almost profitable. It also can't manage without mentioning the oh so low Australian population density, when that does not matter at all. What matters is the corridor and in this corridor with pretty perfect distances of Sydney to Melbourne and Sydney to Brisbane there is a corridor population of 12 mio. That is perfectly fine for such an HSR corridor. I mean the report is contradicting itself when it is first talking about how Sydney-Melbourne is the second busiest aviation corridor in the world and then later talking about how there is no population for HSR, when the HSR would be highly competitive with aviation on such 3-4h corridors.