I remember when I worked at a startup the choice when I got stock options was - pay the tax up front based on the current strike price value - or pay a higher tax when you exercise them and make a profit. If you take the first choice then you'll need to do a lot of paper work to get that money back should the company fail.
If simple well understood businesses (dig up rocks or buy land and build) can return > 10% YoY, why would any intelligent investor poor money into an asset class that has underperformed that in the same period?
Exploration, drilling, construction, exploitation. The early stages cost millions and often lead to failure, with the occasional profitable case and rare super-profitable discoveries. Scaling up costs major capital, after which, prices allowing, a mine can be a cash cow.
There are only 23 million odd Australians, but there is well north of $2 trillion AUD in our superannuation accounts.
Assuming they applied 0.5% of that towards VC, you'd be looking at $10bn AUD of available capital. At least one order of magnitude more than is currently present.
Also, last I checked, stock-based comp in Australia is tax-disadvantageous. I can't recall if it was FBT or something else.