Harry Potter directors came with expirations.
Directing a film is hard on directors. Actors and crew may have whole days, weeks or months offset as they’re not in every scene. Directors have to be there before and after everyone, every dang day. They’re there for pre-production through post. A movie like Harry Potter is full of production elements, all orchestrated, at least in part, by the director. It’s no wonder they went through four directors over the course of the films. Thankfully, all the directors were willing to work together for continuity’s sake.