Some are not. Running a mess hall is in the "not" category; B&R (now KBR) does that really well. Doing and MTT for the entire Croatian army or an Iraqi unit is inherently a government job. I worked for Jim Steele in Panama and saw him in action in both Panama and El Salvador. While I would hire COL Steele to train the Iraqis in a heartbeat, I would not hire Mr Steele or any other retired officer as a contractor to do the same. There is too much capacity to commit the USG in that role.
When I was on active duty in SOUTHCOM and supervising a contract the limits were clear. The contractor had to produce a substative deliverable. While I was a civilian at NDU, I saw contractors constantly producing what I would call personal services even though our contractor went out of his way to try to keep the deliverables substantive. He failed in that, but others were not even trying and DOD simply winked.