I think that's mainly because Hollywood only ever chooses people with a very posh English accent.

我想，主要因为好莱坞只选那些有高傲的英式口音的人。

优雅的英式英语 - SpeakingMax英语口语达人

because the accent's very different from what we teach in South America mainly.

因为口音跟我们在南美主要教的口音很不一样。

巴西的英语老师 - SpeakingMax英语口语达人