some reasons: (I am speaking as a computing grad)

1. Not everyone wants to join government, slow but stable progression & skills you learned are generally less useful. People I know only joined because of their scholarship bonds.
2. 5k isn't considered high for a computing grad (above average yes, high no)
3. They don't have the reputation of being engineering savvy
4. Interview hiring bar is lower (they only care about your grades)

FYI, I am not saying it is a bad place. But definitely not difficult to get into.