[Reeses]

Cities always have an advantage of economies of scale. This means that many products and services cost less in cities

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.

[Alberta's Child]

What costs less in a city?

Triple bypass surgery, to give just one example.

Put together a list of things that you can't even buy outside a metropolitan area to understand the underlying point here.