As someone who's visited rural Texas a large number of times throughout my life, another factor has to be food. There's little cultural emphasis on healthy eating. "Work hard, play hard" extends to food. Nobody would think twice about having barbecue with a Dr. Pepper every day. On top of that, a large portion of the available restaurants in small, remote towns are fast-food, which again, isn't stigmatized like it is in more urban areas. The handful of local restaurants will be barbecue and/or tex-mex.

These factors combine to make unhealthy-eating a simple matter of habit for a large percentage of people in those areas. Even if you really do work physically hard every day, it's not enough to cancel all that out.