There are lots of ways to make income that is not accessible to government recording, reporting, or taxation.
When you're rich, those ways are called "clever".
When you're middle-class, a vanishing species, those ways are called "fraud".
When you're poor, those ways are called "criminal".
Of the three tiers, the rich steal the most, at the least risk and the least punishment. The poor steal the least, at the greatest risk and the greatest punishment.