raywest

Answer: The answer is: "Power." Miss Trunchbull is a sadistic bully, as a school headteacher she can terrorise, frighten and dominate children and teachers. Also the job pays a good salary. She has probably arranged things so the other teachers do all the real work and the difficult jobs. She lives in a house attached to the school, so she gets free accommodation. She can run scams: for example the pupils must be fed, so she gives the catering contract to a company who pay her a "backhander." Thus she has a lucrative job where she does very little work. Plus, you cannot have a story without a villain to be defeated, so Miss Trunchbull is a brilliant opponent for Matilda.

Rob Halliday

Answer: It's a common enough trope to the point where it has become cliche. Stories set in a school will almost always have a teacher or principal (or both) openly dislike their students. Stories aimed at a younger audience will often exaggerate this to an extreme, where the teacher/administrator has a hatred of children in general that borders on insanity.

BaconIsMyBFF