1. Publicly 'owned' and privately operated is most likely a long term lease which is very similar to the private company owning it.
2. The reason those werent privately owned to begin with is that it just wasnt how things were done 70 years ago.
3. In Australia we have a bunch of super funds itching to get involved in these sort of things, which could be done by partnering with one of the many companies that specialise in the field.
4. Eventually it will be privatised, so it's not an issue of the money not being there or the companies with expertise not being there, simply they dont want to pay $6bn+ for it but will gladly take a 100 year lease for $3bn once the government has spent $20bn building it.
5. Major airports in this country are already privatised and charge what they want, as will be the case when this airport is privatised.
6. The cost of this concrete hasn't stopped every major airport in the world upgrading to be able to handle the largest aircraft, including in Australia. The concrete is not the problem.
7. The cost of land? I assumed the government was providing that for free in any case, and still no one wanted to build it.