Vocal tone is one of the big stumbling blocks for many conservatives. The nasal, whining, high-pitched regional speech patterns may sound "authentic" and to a decreasing percentage of voters, but the general public tends to equate "down home" accents with a lack of intelligence. People have become conditioned for the past 4 generations by the mellow speaking tones and neutral accent of the mass media.
Cornball speech patterns make speakers a target for caricature. Sarah Palin, Ross Perot, Dubya, Sarah Huckabee and Ron Paul have all been targets.
Margaret Thatcher realized that the typical British female falsetto tones (so often parodied by Monty Python) of her voice would be a hindrance, and took voice coaching as well as wardrobe consultations when aspiring to be Prime Minister. She understood that people, especially the powerful males reporting to her in government, would not recognize her authority unless she looked and sounded a certain way.
I believe that style of speech is called "Posh" in Britain. It's the speech style of the upper class. There are many dialects of British English, but that is the one people expect from high ranking government officials.
I've been watching videos about British dialects over the last few weeks. Also videos about the history of the English language. I find some of it quite interesting.