It seems like a common-sense answer. Why do police kill people with knives or guns when they could just shoot the gun or knife out of their hand?
The reality is very different than the tv and movie image. Did you know that the nation's leading firearms and self defense experts DO NOT advocate shooting at a person's hand when faced with that sort of threat?
Here's the truth. Under the stress of a life and death situation, NO ONE can be expected to accomplish that. Not even the experts.
In fact, police are taught to shoot in the center of the torso when they are faced with a violent offender because police, just like you, are human. When someone faces them with a gun or a knife, they too are scared. AND, in that situation, there is usually precious little time to act. They must go for the safest bet because if they get killed, who will protect you?
If you think the police academy trains them to handle this, you are right, sort of.
Police academies have a limited amount of time to teach A LOT of law, procedure, and physical skills, and they do a darn good job most of the time! However, there's always too much to teach, and not enough time to teach it.
What does this have to do with self defense? Well if you find yourself in a life and death situation, maybe even faced with a bad guy with a gun, you have to make a decision. If you get his gun away from him, you must shoot, and shoot to kill. Shooting to wound only happens in the movies. In the real world, you shoot to win, and that means shooting, and shooting some more, until the threat is completely over. And that sometimes means the bad guy is dead. And you win.