Roughly 80% of the population in the US live in urban areas. This graphic is already definitely taking the entire metro area into account, which can include fairly rural areas depending on the city.
People are very aware that rural areas are significantly cheaper. They are cheaper precisely because the demand is low. People either do not want to live there, or they cannot live there given the industry that they work in.
You also need to realize that with a more expensive metro area comes higher median wages, so you’re not necessarily even coming out on top living in a rural area.