From my personal experience, the majority of people with strong southern accents in Kentucky came from elsewhere like Georgia and Alabama and Tennessee. Most of the people I've met around here that sport that accent took it up as a way to be "more country" and that was more in the 90s. I really don't hear many strong southern accents like, for instance, out around downtown around campus.
I think the preconception that we're all sitting around spouting yalls in deep southern drawls is mistaken, personally. Its not that it doesn't exist, its that its not as emphasized.