Instant-kills of any stripe in movies and TV are usually bullshit. Sure, instant-kills do exist: blow enough of someone's brain out, and they die pretty much immediately. Decapitation is essentially an instant-death. Severe damage to the heart results in a very quick death.
The issue is, as Axaday implied, that reality is much more disturbing. In reality, people are much harder to kill than movies would have you believe, what with its plethora of single stabs or shots to the gut, for example, resulting in a very rapid death. Strangulation is particularly egregious, which is why when its done in a film as the drawn out struggle it actually is, the result is very upsetting imagery. Real-life Human beings have survived horrendous injuries that would kill most action and horror-film victims 16x over.
So yeah, most people don't want to see that, and networks/ratings boards usually aren't going to allow it.
Edited by CORVUS, 17 August 2020 - 05:39 PM.