It's become such a television cliche that characters who are geniuses, IQs off the charts, smarter by far than everyone around them, don't know what a figure of speech is, nor recognize it when they hear one, always taking the literal interpretation.
Children who socialize with their peers, their families, their community at an early age (even before they start school where they are thrown together with other people) recognize a figure of speech, even when they don't know what it is.
Yet these TV geniuses seem to act as if every spoken word, every spoken sentence, can only have a literal interpretation. In Brennan's case she is a published writer (supposedly an accomplished, professional user of language) yet misinterprets whenever anyone uses a figure of speech around her, and reacts in confusion, and with a need to "correct' the speaker for their perceived misuse of language.
Sheldon in The Big Bang Theory (admittedly a comedy series) does the same, often the comedy stems from his literal translating of a statement.
It's as if these people haven't lived in an English speaking world for all of her life
Similar to this cliche is the flip side of the coin, you have characters like Ziva from NCIS, for whom English isn't their first language, and often attempt to user figures of speech, yet get them wrong, despite having lived in an English speaking country for years now, and surely must have heard these common figures of speech they attempted to use numerous time in their dealings with others or on the electronic media they are constantly exposed to every day.