> A large increase in federal income tax audits targeting the poorest wage earners allowed the Internal Revenue Service to keep overall audit numbers from further declines for Americans as a whole during FY 2021.
I'm guessing low-income people are, for a bunch of reasons including having simpler finances and ~no ability to hire legal counsel or other outside help, way cheaper to audit than those with more money are.
This passage suggests they shifted focus there to keep their total-audits number from dropping even further. The IRS is experiencing a many-years-long deliberately-inflicted severe staffing shortage. IOW this was probably done to keep a metric someone cared about from dropping without requiring more funding, not because it's efficient or just or anything like that.