Governments certainly like to play safe with large and trusted...

Governments certainly like to play safe with large and trusted companies, no doubt about it. Protected is the lowest sec=class, and the classification policy used by AusGov can be hard to understand, especially in a practical way. Defence industry is incredibly large and probably one of the steadily growing sectors, and includes DFAT among many agencies. Everything is out-sourced these days and businesses know that recurring contracts is where the real money is.

You raise a really good question about a real advantage "outside of defence", and you only have to look at the volume of IP theft between nation states and companies. Classification and Defence are synonymous, yet seldom is internal private/public company information treated the same, hence why every month is another data breach.

Cheers