The issue with the glasses may be due to a collision mesh. Having worked with the Unreal Engine 4 I know a little about character model creation. When you model a character (or any 3d object) in 3d program and want players/objects to collide with it you also have to make a mesh for collision purposes. Collision meshes can actually take up a ton of resources depending on the size, shape or number of meshes currently being rendered.A lot of times a developer will just make a boxey or cylindrical mesh around the model to save on resources. That might be the case here. The glasses are basically affixed to the collision mesh and not the character model mesh. It isn't so much about being lazy or doing shoddy work. In some game engines it is necessary to make a lower quality collision mesh in order for the game to run at a decent speed. If you have 200 players in an area and they all have a complex collision meshes your game is probably going to be unplayable, even for a higher end pc.