Why do American movies or TV series, such as The Butler, usually have a British accent?

Moreover, Britain is an old-fashioned capitalist power with nobles who have been inherited for many years, so the British butler industry has a tradition of hundreds of years.

Butler originated in France, but the old British court pays more attention to etiquette and details, and strictly regulates the professional concept and scope of duties of butler according to court etiquette, which has become the industry standard. British butler has also become a classic of domestic service, from which private housekeepers come. Therefore, at the beginning of the world-famous British butler, only hereditary aristocrats and aristocratic families with titles could enjoy it, for nothing but noble royal blood.

When a big family in the upper class hires a housekeeper, they have to hire an English one, which is reflected in the movie.