Tribes & Cities
There is a solid reason for this to be the case. With people gathered into larger communities it is increasingly easy to support people who are not directly engaged in the production of food and other basic necessities. These people, freed from the daily struggle for survival are freed to work on other things, such as developing better building techniques, better tools, or new medicines. There are also economic advantages to cities as hubs of commerce, and advantages of security that high walls and a large force of arms can provide. Beyond these concrete benefits are those of culture and of art, accelerated and fertilised by the proximity of thinkers who can afford to think instead of working in the fields.
While some of these advantages have been left in the past, the economics and cultural attraction of cities remain. Even if for no other reason than the basic Human desire for companionship cities will always be a part of Human existence. Or will they? Many SF settings include technology that would make cities less advantageous, and that even might even create conditions under which cities are no longer advantageous.
And so I get to the recently released game No Man's Sky, and the concept of a post scarcity world. Wikipedia has a pretty good look at the concept, so I won't go deep into it here. Wikipedia uses this definition;
Post-scarcity is a theoretical economy in which most goods can be produced in great abundance with minimal human labor needed, so that they become available to all very cheaply or even freely. Post-scarcity is not generally taken to mean that scarcity has been eliminated for all consumer goods and services; instead, it is often taken to mean that all people can easily have their basic survival needs met along with some significant proportion of their desires for goods and services, with writers on the topic often emphasising that certain commodities are likely to remain scarce in a post-scarcity society.
Many SF settings demonstrate technologies needed for a post scarcity world; advanced manufacturing, highly efficient food production, and access either to enough resources or advanced enough recycling that raw materials never become a concern. Strongly enough, though, few writers seem to take into consideration the impact such technologies would have on the world. There are, broadly speaking, two kinds of post scarcity. There is the more 'realistic' kind likely to be achieved at some point in a our own future, and the less feasible, more extreme example that science fiction occasionally portrays. The more realistic approach can result in a world that while markedly different, still retains the basic political and societal structure that it does today, including things like cities. The latter could result in far more drastic changes.
If large fusion reactors became plausible in the near future this will be a large step toward a post scarcity; the energy excess allowing extensive recycling and otherwise inefficient manufacturing techniques. And 3D printers, while they might eventually move manufacturing out of factories into the home, will still need power. Because such fusion power plants are likely to be hugely expensive and complexed they will be built to serve existing cities, which will then gain an advantage over rural areas that do not support a population large enough to warrant a reactor of their own. This basic argument applies to other technologies that right enable a post scarcity world; it they require large coordinated efforts from a government or similar organisation, then cities remain a valid part of human society.
But take a SF setting like No Man's Sky. In-universe it is possible to harvest elements through a handheld device, and a small spacecraft can carry the facilities needed to turn these elements into technology. If we assume that this technology is a kind of 'replicator' similar to what Star Trek uses is behind this portable manufacturing, and we assume that it can also be used to produce food from the correct raw materials, we have the perfect post scarcity. A single person could theoretically support their own existence without aid from any other individual, and at a level significantly above survival.
In No Man's Sky the megacities and space habitats common to many similar settings are conspicuous by their absence. Instead their are space stations and trading posts that seem to act mostly as hubs of commerce, and fleets of large ships. And this is in fact a highly logical outcome of the technology in the game. There is no reason for cities because they cannot offer any major advantage to those who live in them. Indeed, even the concept of nations and other political entities becomes less certain in such a setting.
If the technology of No Man's Sky was to be introduced into our world cities would not vanish overnight; and might never make a complete disappearance. Because a single person, and by extension a group of almost any size, can support itself without outside aid, there is nothing to prevent those who disagree with their parent society from beaching off and forming colonies of like minded people. In the past it was possible for people to load up a ship and sail across and ocean to colonise another land because they could take almost all their technology base with them. And if this becomes possible again it will happen.
While existing cities will likely remain as hubs of culture, knowledge, and history the formation of new cities or nations seems unlikely. If people are banding together purely because they want to be surrounded by people that they agree with, or share goals with, such groups do not have the incentive to grow larger than the point where it is still possible for everyone to know everyone else. That is not to say that it won't happen, but it will see far more common to see smaller groups. Perhaps communities akin to medieval monasteries or convents will arise; communities dedicated to a goal single goal. It might not be religious in nature, it could be the terraforming of a planet, or the building of a Matryoshka Brain.
In terms of politics it is interesting to note that while war is one of the most compelling reasons for political bodies to exist after a post scarcity has come about, the chances of war are much less. If people can leave their nation and settle somewhere else without becoming refugees dependant on the goodwill of others, they are unlikely to support a war that their leaders have started. Of course wars that the population does support will exist, based on conflict between variant cultures, but wars of economic or political convenience will be much less likely.
It is worth pointing out that the separation between what exists in the No Man's Sky universe and what might become reality in our own is a spectrum, not a vase of two discreet options. It is the details and exact scale of the technology that will determine the size of the groups that form, and how far they spread. If restricted to Earth the spread will be much smaller than if the whole galaxy is opened up by FTL travel. Micro-nations are a plausible middle ground, with the practical advantages of a political entity, and the freedom of a smaller group.
So while there is considerable debate over No Man's Sky as a game(I haven't played it myself), it is interesting as an example of one possible future rarely explored in SF, despite being well within the limits of common fictional technologies. While many SF settings unthinkingly reuse the tropes of other works, creating huge sprawling cities and urbanised planets, it would be good to see more variety; diverse nomadic societies rather than an unimaginative ecumenopolis.
So while there is considerable debate over No Man's Sky as a game(I haven't played it myself), it is interesting as an example of one possible future rarely explored in SF, despite being well within the limits of common fictional technologies. While many SF settings unthinkingly reuse the tropes of other works, creating huge sprawling cities and urbanised planets, it would be good to see more variety; diverse nomadic societies rather than an unimaginative ecumenopolis.