How much revenue was ever gained by such audits?
I mean, sure, look out for suspicious patterns, put things in the code that need activation or registration or whatever else, especially for your major expensive pieces of software. You at least need to get an idea that something is being used without a licence, and on what scale.
But how often did that lead to a company that then was audited, found wanting, coughed up and continued to use the software afterwards in order to get follow-up licensing? I can't imagine it's a profitable enough venture to even pick up the phone to the lawyers to start the process (I imagine the businesses that did cough did so voluntarily nearly as soon as they got a call and the others told them to bugger off and get a warrant or similar).
I never saw the economics of it. Microsoft still have it in their licensing and I can't think that it would be worth it. Those places doing such things would cough once and then use that as incentive to migrate, rather than cough up every year or whatever, surely? That's after all the places who just resist it, quickly delete all their copies, or disappear into bankruptcy rather than pay up, and the costs associated with cutting through all that to some evidence.