A French accent isn't that hard

A French accent isn't that hard and there is such a thing as French actors (and there is even such a thing as unpretentious French actors) so I don't understand why some movies have people speaking with a British accent when the character is French.  If it were an all-British production it would be more understandable but even the American actors put on a British accent. Almost everything is in English except they will say "monsieur" and "mademoiselle" instead of Sir and Madam and French proper names, some or all written text, and the names of locations are said in French.

They could simply make the point that the setting is France with a graphic in the beginning that says "Location : Paris, France" and then carry on in English. Or they could do it in French and subtitle it.

I assume the reasoning is due to one of or several of the following :
a) A shortcut to let it sound foreign and yet understandable.
b) Hollywood has a very, very poor grasp of geography.
c) A ploy to piss off the frenchies.

A couple examples from the movie Hugo (2011)  (keep in mind that every single character is supposed to be French) :

As I recall, another example would be the 1998 movie version of Les Misérables which had a mess of accents, mostly not French – specifically, Liam Neeson didn't bother putting on an accent and Claire Danes' French character alternated between an American and a British accent.

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It's an interesting poster/mural from the movie Hugo.  A globe, a chubby body with something exiting his heart, a blob and a VU on either side. It looks vaguely familiar but I can't place it. I'd love to know what it is.