I think you have hit on several of the contributing factors. I believe the leading cause is definitely socioeconomic, which then carries in to culture. The poor often buy foods that are cheaper and processed so they can afford to feed the family, then on top of that they fry the foods because it's an inexpensive way to increase satisfaction and calorie count.
Much of those fried and smothered type recipes originated in the south during slavery because quantities and supplies were absolutely limited for slaves. The foods stuck around but the south tends to be MUCH more sedintary than it was then.