I suppose you could have hand cut singletrack for all of the trail networks, but you come up against a few issues.
1: It's all volunteer built, and therefore, takes forever to build, will vary quite a bit in quality as it's hard to find volunteers with good trail building experience. In the end you will quite likely have a poorly built trail, with tiny features, if you manage to get much built at all.
2: Get a contractor to hand build it. Yes, it would be significantly quicker, but compared to machine cut trail, it's still massively slower to build, plus it is very labour intensive and that would make it extremely expensive.
Places like Canada and the US have had a couple of decades of trail building in front of us, a way bigger population to pull from when it comes down to trail builders and some many very well established trail advocacy groups, like IMBA, NICA, TORCA, WORCA etc.
You look at an area of similar size in the US and compart to say Tasmania and it dwarfs the amount of trail we have. And that basically comes down to population and the time that they have been building trail. They do have a big amount of shared trail though.
One thing I think that Australia would benefit from is a nationwide trail advocacy body. An organization that can help source funding, give guidance to clubs and other not for profits that would like to develop new trails. Auscycling only cares about racing, so apart from local councils, there's not many organizations doing any big trail projects. Sometimes the problem with a council run project, is that the council employees aren't experienced in designing a trail network, so they rely totally on the trail building company, and don't always get the best outcome because of it due to that contractor not knowing the area like a local would. If you had a national advocacy body with state and regional groups, they could assist any government bodies or clubs wanting to build a trail network and provide advice on the best approach.
