It's been a part of the game for too long, I doubt it would get changed.
It might not be identical to 'real life' but it acts as a consequence for getting decapped.
It makes players try to be defensive to avoid a decap, or vice versa, with players striving to decap their opponent to gain the upper hand.
And say if you got your foot blown off by a shotgun, your whole body would react to the pain from the injury, not just the leg attached to it. Your muscles might contract/convulse as a result of losing your foot, instead of relaxing entirely, but for the purpose of the game it seems proper that you are 'reset' and lose your possible advantage.