A few weeks ago at the Signature FBO at IAD, while waiting for my passengers to arrive I watched as a mobile lounge docked with a Luftwaffe Airbus. Not sure why they provide this service to the German Air Force, but not to civilian Airlines.
That's because it is not a passenger flight, and thus doesn't have a passenger gate. That A310 (A300?) is a regular commuter between Germany and the US capital, but it doesn't have a gate since it isn't a passenger airline. It parks off to the side at a FBO and the pax are shuttled in.