IR Hold with G1000
I would suggest that's because that section of the test was likely to be examining the ability to fly the hold on NDB data not GPS data. Therefore LZD needed to be the primary source.(By all means I'd use the GPS data as well as a back up if there's the capacity but not as primary in that section of the test.)
The RNAV approach later was testing exactly that - the use of RNAV GPS driven data and procedures.