We don’t have a system that allows us multiple options for the head when equipping an item. It’s either we keep what you have hairstyle wise or we override it. Many of the hairstyles break (pig-tails being a main offender) through the mesh of the head item which means we generally resort to an override :(
Hopefully in the future we can get more options so we can preserve the hairstyle. I agree that it looks a lot better :)