Why haven't they...

[MacMillan of Rathdown]

Citing examples of these movies would be of interest.

Rather than recite dozens of films I'll give you just one example: The Great Dictator, released in 1940. This was Charlie Chaplin's first all talking picture and, although nominally a comedy, in it Chaplin departed from his usual slapstick to include satire and social commentary. In the film he plays the dual roles of a Jewish barber in the ghetto, as well as Adenoid Hynkel, dictator of Tomania. Hitler's entire entourage is brilliantly satirized, as is his chief ally, Mussolini-- in this instance "Benzino Napaloni", the dictator of Bacteria, as played by Jack Oakie. The satire and social commentary was not lost on American audiences, and for the first time since the war had began, grass-roots Americans began to be openly hostile toward Hitler and his regime.

Well Gibson can get away with things that many others cannot. He constructed an English villain full of ambition to be the "bad guy" and nobody likes a rotten apple. I look forward to a movie featuring Benedict Arnold.

Just as soon as I finish the musical version of Oswald Mosley and Lord Ha-Ha In Love I'll get right on it.

Simon Callow was RADA trained but he then had to do a silly American accent so he would sound more German. Only the Italian parts were allowed an actor with an English accent. However Americans like F. Murray Abraham managed a passable English accent (ah but he was playing an Italian wasn't he!)

That, Trefor, is called acting.

Yet Hollywood still likes to use British film studios to make some of them.

There are a couple of reasons for using British studios:
1) The crews speak English, and work to an American standard.
2) Because very few films are produced in the UK it is often easier to get studio space (ie: sound stages) in the UK than at home in Hollywood.
3) Financing. Because the money comes from all over, it is sometimes necessary to give a film a certain "domestic" content in order to give investors a tax break. A film shot in the UK qualifies for all sorts of EU tax advantages because of its "EU content"; that is the percentage of the films budget in time or spend that takes place in the EU.

It is, however, the exception to the rule when they do not "take liberties with history."

It's called Dramatic License, and it goes back to the days of Shakespeare. You remember him. He was English, and he never took liberties with history. Did he?