Why do many televangelists talk abnormally on television?

Many televangelists talk loudly and shout as if their congregations were hearing impaired, they speak in a contrived and staged way, or some of them (the back-woodsy types) gasp for air every seventh word? Why can't more televangelists talk like normal people? I realize that this may sound like a dumb question, but I am sincerely curious!