Military Special Operations to OCS?

Why is that when an enlisted Army Ranger or Special Forces Operator goes to OCS or does Green to Gold he doesn't automatically go back into the 75th Ranger Regiment or Green Berets? The man has prior enlisted service with a Special Operations unit and the Army is just going to waste all of that man's Special Operations training in something he doesn't want to do like Signal. I know he can branch Infantry but that is still taking time away from the Green Berets or Rangers.