Why isn't he facing execution if convicted? He deserted to the enemy - in wartime. Try the little shit, convict, and put him up against a wall. Hell, I'll pull the trigger myself.
Politics.
Those charges were VERY carefully picked to take execution off the table.
Someone, unusually, has realized that Bergdahl must be seen to be dealt with, for the sake of the army as a whole. Yet they can't even imply the Worm was wrong in doing that stupid bleep swap. you know how it goes - you spend more time and cunning fighting the brass and their higher ups than you actually do dealing with the enemy.