jorgem has it right. If you can get your mind around how complex it really is to make the entire wheel hollow with ribs inside with the flowing spokes getting wider as they get closer to the hub area while at the same time the wall thickness is increasing this can not be produced with "injection molding" 3D Printing can make duplicate the shape but the printed wheel is too weak, takes a lot of hours each to make and costs way too much.

3Drsr Technology sets designers free to make amazingly complex hollow structural parts quickly and at reasonable cost.