Should've watched ER instead :p (at least the first few seasons).

Just from recent memory and a few that I dropped after the quality plummeted: The Mosquito Coast, Barbarians, Westworld (Nolan and Joy remained showrunners but they changed the writers every season). It's also pretty common for Amazon originals, it happened to The Man in the High Castle, Goliath and recently Carnival Row.

New, mediocre writers. Like many shows these days it followed the trend of changing the showrunners and the writers room from season to season, that's why it's so inconsistent.