I think it's more of a player first then ai. I came across friendly fire in enemies protecting me from getting damage. It could be said that if the enemy then turn, and then freeze wouldn't have suited the developers difficulty of the game.
I guess my point is that the point of the turn weapon is often to use the planned enemy move to hit another enemy. If the enemy just freezes and never turns the turn weapon with freeze effect is essentially turned into a 'freeze' weapon. I.e. the turn effect is entirely gone.
