Why does the military shave recruits heads? because you are a maggot...Untested, untrained and unable to have any privy's as a maggot...
When you're in the field, your head is always covered anyway. Anytime you are outdoors you need cover on your head (ACH or standard cover).
Because if they shaved their privates privates, people would complain, so they shave their heads instead...
In Germany heads were never shaved when you enter military. Not in the past and not now. So this is an american thing.