I'm not saying this is fair, or accounts for the full amount. But there are things like R&D tax kickbacks companies can get, which are designed to incentivise companies to do R&D in Australia. There are probably other kickback incentives. Now, do I think these companies could (or should be able to) legitimately tally up these kickbacks to net a nil tax bill - no, probably not. But I'm not even close to an expert