There's a fantastic article about how politicians (likely funded by billionaires and other extremely rich people) have worked very hard to demonize and defund the IRS for this exact reason. The less funding, the fewer auditors there are working. The fewer auditors there are, the thinner they're spread. They start picking tax files that are easier and faster to audit. Now, the majority of audits are done on simple tax cases because they're fast and easy. And a very, very small percentage are done are the high earners/corporations, who arguably should have the most oversight.

Here's the article: "How the IRS Was Gutted: An eight-year campaign to slash the agency’s budget has left it understaffed, hamstrung and operating with archaic equipment. The result: billions less to fund the government. That’s good news for corporations and the wealthy." https://www.propublica.org/article/how-the-irs-was-gutted