All of the above (except lower costs, not a thing for anything in Australia).
In particular, in essentially all (non-chain-fast-food) restaurants where you can get a meal for less than $10, nobody is making award rates. If you're lucky the staff is family, if not they're exploiting students or illegal immigrants.
With higher prices for restaurant/café meals?
With less competition?
With lower costs for other inputs?
With greater demand for labour across the economy?
By illegally paying employees below award / not paying superannuation payments?