Until science comes up with the real world Star Trek Phaser (locked on the "stun" setting) there is nothing that will physically stop an attacker that does NOT have some risk of death to the attacker, other than the attacker's free will.
Its all word games, to a degree, but words do matter. "shoot to kill" is a very clear statement of intent.
There is a difference between shooting someone to stop them, and they die as a result of the force used stopping them, and shooting someone with the intent to kill them.
In our society, it makes the difference between justifiable self defense and the crime of murder.
Are the police being trained to commit murder? No. Despite the rhetoric used by various activists claiming otherwise to further their agenda, cops are not trained, nor sanctioned to commit murder.
The training is to employ deadly force, when necessary, in order to stop the immediate threat. Death MAY result, but it is not a certainty. It is a high probability, but not a certainty.
The opposite side of the coin is supposedly "nonlethal" force. There is none. People use the phrase "non-lethal" or "less lethal" referring to stun guns, beanbags, rubber bullets, and even the old fashioned beat them with a stick.
But all those things have resulted in death. They USUALLY don't, but again, that's not a certainty.
Taser someone with a (possibly unknown) heart condition, they may die. Wound someone? Nick an artery and they may die. You don't intend to kill, but death could be the result.
We shoot to stop, in "gravest extreme" knowing that death may result. We don't "shoot to kill".