I don't think they're measuring the _value_ of the work, just what it would've cost to have humans do it. How long would it take you to produce a report of a specific length on the history of changes to the White House approved by presidents over time that includes citations and links to sources? Let's say 40 hours? Boom. $100 per hour * 40 hours = $4,000 report and 1 weeks worth of effort produced in 15 minutes. Multiply this type of "work" by 400 and you have $1.6M in labor costs and 7.6 years of work.