The center post is fixed (not a bobbin-type shuttle) and engineered to hold the most thread and give the shuttle unit stability.
The thickness of the silver used to fabricate the shuttle is a compormmise between too heavy and too thin to acheive the proper balance of weight. This ensures the shuttle is comfortable and balanced to use, and yet is strong enough to prevent unwanted bending.
The beauty of sterling silver is that the blades can be adjusted so that the tip tension is perfect for the size of thread choose to use. You don't have to put up with a shuttle that frays/cuts your thread, just adjust the tips so that the tension is not so great. One strategy is to leave one tip open, untensioned and adjust the other tip for the size of thread you choose (closer points for finer thread versus points farther apart for thicker thread).