> What is the motive [...] What’s in it for them?
There's a huge monetary incentive, since things like social security payments (the largest item in the federal budget) are inflation indexed. The Boskin Report [1], which argued that inflation was overstated by 1.1%, estimated that their proposed "corrections" would reduce the deficit by $202 billion by 2008.
The whole thing was rather suspicious in my opinion. The report was based on some questionable interpretations of inflation, and it seemed like the Senate appointed particular members in order to get the outcome they wanted, as Thomas Palley argued [2]:
> The commission is itself a delicious example of such bias: All its members were on record prior to the establishment of the commission as believing the CPI to be overstated. At the same time, the commission took no evidence from such well-known economists as Janet Norwood, a former head of the Bureau of Labor Statistics, and Dean Baker, of the Economic Policy Institute, who believe that the CPI provides a reasonable reading of inflation. In effect, the commission took account of all the evidence of overstatement of inflation by the CPI and downplayed the evidence of potential understatement.
[1] https://www.ssa.gov/history/reports/boskinrpt.html
[2] https://www.theatlantic.com/magazine/archive/1997/04/how-to-...