1. Because Paizo doesn't know how guns work, and
2. All the punch gloves presumably work the same, the way starfinder weapons work is that each weapon has like 5 different variants (tactical, advanced, elite, etc.) with different prefixes that work the same but do progressively more damage because the equipment treadmill wasn't extreme enough in pathfinder, apparently. The "Paragon Shell Knuckles" cost 130 times what the cheapest variant does, and in exchange does 14d8 damage a punch.