Earlier quoted context omitted.
I feel like I'm not understanding your comment. Is it that you don't want IRS employees sitting around doing nothing? Because if this resulted in losing $34B in revenue, it doesn't like they were sitting around doing nothing.
At some point, you'd start spending a lot more money to recover less money. You'd probably be wise to back off at that point... "diminishing returns". We're not there, though.
I suspect that's true, but you don't actually know that from this dataset. Some portion of the cost is born by the auditee to respond/defend against the audit and passed on to shareholders/employees/customers.
If the response costs are great with respect to the IRS's audit costs, the government could quite profitably add auditors, but have a negative overall impact on end citizens.