system
Given the following post, respond as if you're commenting on Reddit:
human
[Pathfinder] Why does charisma replace constitution for undead?

As a reminder, I'm not looking for a Doylist answer. The merits and reasons from a system perspective is not what I'm asking about.  

Wondering if there is some kind of magical, biological, or universe reason that charisma governs some of the physical aspects of the undead.
gpt
A possible explanation: Undead are held together by arcane energy, which is governed by their willpower, not by their physical bones. The dead bodies are not the actual actors, as live bodies are, but rather just meat sacks that the necromantic magic moves around. Thus, the meat sacks themselves have no bearing on the magic.