Since they will be paying the 30% FairTax on every item.
The Fed govt doesn't pay sales tax now on items they purchase. I see no reason for them to do it with the Fairtax either.
Read the bill, it's another part of the scam to make the Fairtax rate lower than it really is. The government pays 30% FairTax to itself and counts it as revenue. Another double-counting error by the FairTax crowd...