Contracting him could easily still be cheaper than having him still be in.
Contracting is really for short term needs. You pay short term wages (which bundle in insurance, retirement, profit, etc) for contractors. However, if the organization will continue to have that same need for several years, then paying people short term wages for that long is very expensive.
My impression is that very little about the military is voluntary. If they need pilots to fly different craft, the pilots will fly different craft.
When that happens, they take the most junior folks in the grade and force them to retrain into another career field. They give you a short list to choose from. Most of the jobs are special operations and aircrew. You have a short period of time to make a choice and submit a package. If you don't act, they pick one for you. They picked airfield management for me near the end of an enlistment that earned me a 5.0 SRB when I re-upped as a 3C072. I self-promoted myself to Mr, instead. This was in 2008. The Air Force has been bad at staffing for a long time.
Once you have volunteered, the needs of the service are what matters. They attempt to accommodate, but in the end if they need you somewhere they're going to put you there.
How can that possibly work? How can you force someone to retrain into special operations? How does anyone build the motivation and determination to pass the qualification courses for that when they don't even really want to be there? Why would special operations even want someone who wasn't remotely a volunteer?
The military isn’t all sir-yes-sir as people think - if you don’t want to be there then they don’t want you to be there either.
E: forgot special duties were an option, too. If you applied for and were selected to be something like an MTI, MTL, or recruiter then you didn't have to retrain. I'm not sure what would happen after the special duty was done. Usually you would return to your career field once you're done, but I don't know if that's the case if you do the special duty to avoid NCORP retraining.