There are thousands of good reasons why magic doesn't rule the world. They're called witches and wizards, Magrat reflected, as she followed the other two back to the road. It was probably some wonderful organization on the part of Nature to protect itself. It saw to it that everyone with any magical talent was about as ready to cooperate as a she-bear with toothache, so all that dangerous power was safely dissipated as random bickering and rivalry.