So, it is the 26th century, and you are a terran soldier in the military. You made some stupid mistakes in Delta Scorpion, and ended up with inner organs becoming outer organs. You never read your contract, which stated any human that died in combat can randomly be selected for the CYBORG PRIME program. You get decked out with a metal skeleton frame, a robotic heart, a super action rocket mounted laser fist, and you get shaved. All corpses that are sent to the CP program are shaved completely(head, eyebrows, nose) before they get their augmentation. My question is, what is a plausible reason why this is done?
As @Erik has already stated, it reduces the chances of complications due to loose hairs during the numerous surgeries required by the CYBORG program, particularly those involving the noggin. It's the same reason they shave patients going in for brain surgery - make's it easier for the surgeons to see what they're doing.
As an additional note - maybe some of the drugs used in the program are similar to chemo drugs, and have hair loss as a side-affect. Bringing someone back from the dead is a gnarly business.
Maybe it's just less upkeep and maintenance for the cyborgs if you don't have to worry about cleaning and trimming their hair.
Maybe one test subject had lice that got loose and infected the program, so they just went scorched earth and shaved everyone.
It is very plausible to remove all external hair before a surgical intervention in our days.
Before every surgery all the hair is removed from the spot. If a hair drops in the body it may cause an infection because the body may recognize it as a foreign body. Even if it's a corpse, they will be living organisms again, and as long as they are not complete robots, the problem may stay. Note that the body itself is covered with a lot of hairs that may not be visible.
I would also suggest you reconsider the shaving. It is a very old technique that holds the risk of cuts. Also the roots of the hair will stay. At my last operation I heard the nurses point that out. They said that nowadays (and that was like five years ago) we have a lot of alternatives that would do a better job and called shaving "barbaric" and "old fashioned".
The top brass wants the other troops to see the cyborgs as equipment, not as people. Expendable equipment. That will be a problem with ex-human resources, and especially human-looking ones. So what can be done? Shaving the head is one little step in that direction.
Compare this story about bomb disposal robots, and how much bother it was for the repair staff.
The most obvious reason would be that it reduces the chance of any hairs getting stuck inside the metal parts during the grafting process. That might cause weird defects later, and since the dead aren't going to object, removing everything that might get trapped and make the cyborg program less likely to go wrong in some way sounds like a good idea.
If they already go into so much bother, wouldn't it be easier to just replace the entire body and keep only the brain? If these cyborgs are used in battle, every part where metal meets living flesh would be prone to separate or tear, and the flesh would get bruised or cut up just from metal parts moving against it so much. (I'm guessing your battles involve a lot of body movement, they aren't just sitting in a chair driving a battle mech or something.)
So it's not really a question of being shaved, more a question of people not bothering to give body hair to a cyborg, even if they make them somewhat human-looking on the surface for the purpose of getting the civilians to co-operate with them easier.