The ATO now has very complex models for different businesses and know by your inputs what you should be making and paying wages. Yes if your running a bar you can go to Dan Murphys, the market etc and pay cash but more and more will get caughtMost small businesses, especially those in retail and hospitality, pay a large proportion of their workers cash in hand. They pay a bit extra per hour (maybe a dollar or two) and don't have to worry about super, sick leave, annual leave, workers comp (even though their staff are still entitled, they think they're not or are too scared to claim), payroll tax, unfair dismissal claims etc etc
Most workers don't really have a say in the matter, it's either accept the cash in hand job or keep looking for work in an industry where cash in hand work is endemic.