That's simple. Most gunslinger gear uses mundane TTS and general weapons control & interface upgrades to boost gun performance, but once you get to 5-star rating the technology can't really be stacked any further with reasonable efficiency, and the hats alone give the maximum practical benefit. At this point, it becomes necessary to use more exotic impulse amplification and enhanced exoskeletal actuators to gain any further benefit such as greater recoil bracing for heavier loadings, faster articulation or such. This requires sophisticated powered reaction wheels, which unfortunately add significant bulk and weight. To get the most possible benefit from this cost, they are thoughtfully engineered to also hold important combat provisions such as some of the more common munitions, teatime snacks, and condiments, and allow them to be fresh-ground at need.