Why do most death spells do 10xcaster level damage on a failed save rather than just kill? They're Death spells, not "a lot of damage" spells.
- In Universe reason: death isn't a binary state (the exact point someone dies is more of a philosophical question), so an instant kill spell would have to be a "does a tonne of damage, which would kill most things" spell. Out of universe reason: An Obvious Rule Patch intended to stop players just killing any random thing with tonnes of HP that wasn't explicitly stated to be immune to them (also preventing it from being a Useless Useful Spell which doesn't do anything to anything worth using it on).
- This also stops death spells from bypassing Regeneration, which is a common and divisive rules argument in the Dungeons & Dragons version that Pathfinder is based off of.