George R.R. Martin, giving writing tips and sliding into Game of Thrones show trivia:

Funnily enough, the show has been killing a number of minor characters who are still alive in the books, such as Daenerys’ two handmaidens. When I approached [the producers] about this, they explained to me that unlike my book characters, the actors expect to be paid money! Therefore, in order to introduce a new character at the start of each season, they’ve got to kill some of the old characters off.