A big part of the problem is simply that rural areas are less densely mapped. Though both draw from the huge trough of data referenced above, cities generate a huge amount of location data from street grids, businesses, addresses, and constant user activity, while rural regions can have fewer marked roads and named landmarks. That means Google Maps has less raw material to build a highly detailed picture of where you are and where you need to go. Because data on rural areas tends to get updated much less frequently than data in more populous areas, major changes in routing or addressing often aren't reflected in the current version of the app. It's an issue you encounter frequently on Street View when perusing rural areas; sometimes the images are as much as a decade old or more, showing buildings that no longer exist, house different businesses, or have been renovated to look drastically different.