Actually, there is no need for blue cities or even red cities, or cities of any size.
In today’s world, there is no need to be next to or close to the services which people sought when transportation or communications was either slow or non-existent.
Cities are a thing of the past, and there is nothing that people get from a city that they can’t otherwise get from a small town or village or suburb.
Let all big cities die and let’s get back to living without all the headaches.
Every time I see comments like yours, I am reminded of a novel named “City”, written by Clifford Simak and published in 1952. It’s been a while since I read it; I will have to go into the basement and find the paperback.