Cities always have an advantage of economies of scale. This means that many products and services cost less in cities simply because they are sold in larger quantities. In some cases cities have things that rural areas don’t have at all — like prominent universities, major league sports teams and specialized medical care.
I honestly can’t say I know of a soul who lives in a city because it’s cheaper.
What costs less in a city? An economies of scale graph is a curve, not a line, and has an optimum, beyond which costs go up.
The optimum population density on a number of measures is around 400 people per square mile, not 400,000.
“Cities always have an advantage of economies of scale.”
Part of the problem is that this concentration of people is also a concentration of power.
For example, here in the DC metro area, there are enough people to force the rest of Maryland and Virginia, and even the rest of the country, to pay for and subsidize the riders of the subway system. I can see the need for it, but I have a hard time accepting that all of this is built and run on expectations of receiving funds from outside the service area, but with little input from the outsiders. I understand roads in rural areas are beneficial, too, but the population centers control the spending for those also.
What we’re talking about is called “internal colonization”, where the cities control the distribution of wealth gained from the entire country.