>>8388297The designed it to look appropriate to the comics, where the Silver Centurion has a fat neck that feeds right into a bulky Chestplate. They sacrificed neck articulation to get it right, they probably didn't even give consideration to a special neck joint for a Tony Stark head.
It's like asking why the classic Iron Man didn't come with an 80's era Jim Rhodes head. Why is our only option the 90's flat top hair Jim? Answer: extra expense that only a small amount of fans want. The Legends is a budget-friendly toyline, they rarely go the extra mile if they don't have to.
