Imagine a world, in which when you teach something to someone the knowledge is considered your “intellectual property”. Your students are not permitted to teach the things they have learned from you to anyone else, neither for money, nor even for free.
To become a teacher, one must buy into the guild for a lot of money, inherit rights from someone who was a teacher, or teach something that hasn’t been learned from anyone, i.e. something newly invented.
Being a teacher was a very powerful position. Having a monopoly to teach and usually even your own districts to educate exclusively, a teacher could charge any price. Furthermore, teachers even had the right to dictate the purpose and conditions on which the knowledge they taught was allowed to be used.