The choice of a turboprop solution was driven by the need to perform Sarajevo approaches (aka Khe Sanh approaches), or so I was told at the time.
With it's inflight deployable thrust reversers and speed brakes, C-17 can make an approach far steeper than the Sarajevo approach. In addition, the C-17 can land using up to a 6 degree glideslope (normal glideslope is 2.5 to 3 degrees) on final (steeper than a carrier landing) with NO flare and do it into an unpaved field. And C-17 has turbofans, so that is not an issue for a properly designed turbofan equipped military transport.