There's a big difference between acknowledging that you owe taxes but not paying them, and lying that you don't owe taxes when you really do. I can only sympathize with people who do the former, and these audits are all about catching the latter.
The audits also catch a lot of cases where people don't know how to file anything beyond their basic employer withholdings. If a poorer, less educated person gets a 1099 for a side job or does an early withdrawal from their IRA, they are likely to fail to report it properly, or pay the required taxes. This is not usually intentional, they just don't know better. Even if they know they have to pay taxes on the money, they don't realize that the IRS didn't already take their cut just like they do from a paycheck.
True, and the IRS is fairly reasonable about understanding when something is intentional or unintentional when levying fines and setting out payment plans.