Could this be why they moved to Bedford County?

Another increasing problem was that tobacco was extremely exhausting to the soil. After three years of being harvested, the tobacco had exhausted the soil of its nutrients, leaving much of the land worn out and of no use to farmers. For example, in Montgomery county, by 1783 much of the land had become a relatively barren landscape thus forcing many people to move on in order to have any opportunity of succeeding economically. In order to solve the need for more land, many settlers bribed the Native Americans into taking pots and pans and other various items that the natives had never seen before. In exchange for these novelties, the natives lost control of ancestral lands in and around the Chesapeake region. As a result, the colonists were able to take away the natives' land without much resistance.