This is also true. However, the centralization causes various forms of impoverishment -- which you might also describe as "specialization." Cities develop zones around them that lack many services, but concentrate others. Think of the places where there are lots of warehouses. If you are in a city to be connected to some kind of a hub, the fact is that not all of that city's area is going to be equally well connected.

Think of what happens to towns near large cities. This has been studied by social geography since at least the 70's.

> That still doesn't have anything to do with the discussion.

Cities often act like businesses. In the U.S. cities even incorporate, just like businesses do. The "shareholders" of a city are usually its property owners who vote for city leaders who implement supply-side policies that raise property values and rents in the city, such as zoning restrictions, and demand-side policies like concentrating services, as the previous commenter mentioned. If the city is the leading commercial city in a country, it may even influence central government immigration policies, which can further increase demand for property, a.k.a. the city's "shares".

It makes a lot of sense and has everything to do with the discussion.

Not exactly a desert. More like zones of coalescence, like areas cleared out inside a nebula that's a stellar nursery. You're not going to find every single kind of service in those suburbs. You're not going to find certain kinds of businesses. Anything that benefits by being well connected to a hub is going to be drawn into that hub, which means that other areas of the city may have less of it.

By "impoverishment," I don't mean "becoming poor" in an absolute wealth sense. I mean that certain things are sucked out of certain areas to other areas.

And make a ton of money while doing it! Farms closer to cities are richer than farms further away from cities.