I don't think this is a silly suggestion. This is a realistic game because of the level of interaction, and customization of moves you have with the character. Most mods have toris with human joint design. The range of motion each joint has is based in realism. If your elbow or knee breaks, it will flop around. If your wrist breaks it will flop, but your hand should continue to work?
Fractures in this games are really more like dislocations. if you dislocate your wrist you don't necessarily lose finger function.
(Also spars are popular because they display skill and floridness not realism.)
Adding this feature would cause a real shitstorm in aikido mods when people do wrist locks as openers. As soon as you have someone in wristlock, it's not hard to break their wrists, and if they then can't grab, they're fucked.