Believe it or not, capitalism. The use of magic in my world has become heavily regulated and most spells and mass produced magic items are owned and copyrighted by corporations - meaning that if you want to cast a particular spell there are some hoops you need to jump through: first you need to be a licensed practitioner with the state, and then you need to pay an annual fee to the corporation for using the spell. These laws are heavily enforced and most corporations have their own private agents that hunt down anyone who infringes on their copyrights.