How come there aren any spells or techniques that cause instant death?
This relates to the concept of damage, and hit points which represent damage sustained. To instantly take all hit points away (or worse, ignore them) without a random roll is a detriment to this model, and is usually done for a secondary agenda. This might be a scripted storyline, where a particular event must happen, or it might be because a particular character or creature doesn’t fit well in the model. In any case, if it can be done without “instant death,” all the better.
