We don’t need to have everything explained by the film. There are other non-film sources with which to draw on for relevant information to people who would care.
Those other sources aren’t canon.
Then why do you care? Why do you want the film itself, by itself without external sources, to explain everything when the film is already over two and a half hours long?
Most viewers don’t need characters to exposit information only relevent to the hardcore fandom. Especially when this is fantasy, not science-fiction.