Yes, one of the group (I'm sure either France or Germany) insisted it had to be a prop, either for tactical reasons (Being able to reverse on rough ground springs to mind) FOD....
C-17 has turbofans and can back up an unpaved 2% slope at MTOGW into a 25 knot tailwind. So that is not an issue if the nacelle is designed right. The reversers also are deployable inflight to enable VERY rapid and steep descents. As for FOD, the C-17 operates routinely from unpaved austere fields and has had no significant FOD issues, and that too is largely due to careful nacelle design. In many ways, the C-17 nacelle is much more unpaved field friendly than any turboprop can ever hope to be.