In the 1980s and before, the IRS literally had no way of knowing if you're telling the truth without auditing you. Everything was done on paper, cash was king. So the audits were indiscriminate and invasive, and needed a large army of employees to orchestrate.
Now, the IRS knows almost everything about your finances. They get electronic data from your employers, your bank, your brokerage. Most of commerce is settled electronically. Paypal and Venmo send them your info if you receive more than $500 in a year. There is nothing to be gained by randomly auditing the average family if the numbers on their report match what the IRS knows. The IRS can zero in on specific activities, such as people claiming unusual business deductions. But they no longer need to routinely audit most of us, and they don't need funding to that effect.