I think you don't quite understand how things work. 5G may be efficient but the exploitable bandwidth is still limited. In cities the density of cellular mobile communications antennae is higher which leads to a reduced areas covered by a tower in which subscribers have to share the bandwidth with others. Also, in cities as opposed to rural areas, even when the bandwidth is shared, the users of a given area are often just transient. The conclusion is that the urban network quality is different from the rural one and that it (unfortunately) adds up as another reason to flock to a city.