Anyone got a good reason?
Because it looks stupid having every square inch of land covered in city tiles. The AI puts cities so close together that they end up touching each other by the time they hit level 4. Back when we were all discussing city placement, everyone, including the devs, thought that cities should be spread out and that they should be important and valuable. The inspiration for this was all the fantasy and rpg games where you're questing in a kingdom or empire. Those kingdoms and empires would often only have one or two Major cities while the rest were small villages or outposts. Think about the old school Final Fantasy games, like Final Fantasy 3 on the Super Nintendo. How many Major cities were there? How far apart were they from each other? Often you needed the air-ship to travel from city to city because they were so far apart.
The way things are set up in game now, the AI and players both spam out cities. We also end up building every single building in Every city. That's not good either. It really de-values the cities. None of the cities seem different from one another with the exception of a city that might be near a magic shard. It just seems really bland and generic and I know that's not the feeling the devs wanted to achieve.
To really make cities matter we need to be able to Specialize our cities. Just like in Gal Civ 2 when players specialized planets for certain tasks we should be doing the same thing in Elemental with our cities. Some cities should specialize in certain tasks based on what resources are attached to those cities. Cities with metal deposits attached to them should concentrate on mining and making weapons and armor. Cities with food resources attached should specialize in growing food for feeding your growing empire. Cities with magic nodes should specialize in in research. This places a much Greater Value on cities. If you loose a primary city that's bringing in the majority of a needed resource for your kingdom could end up crippling you, and That's how it Should be. As it stands now if you loose a city, unless that city has a rare resource attached to it's ZOC, it's no big deal if you loose one because your other cities do all the same stuff the city you lost did. Does that make sense? Not really, not to me anyway.
Strategy is the most important reason of course, but the second most important reason why city spamming is bad is simply aesthetics. When you play any type of fantasy game or a rpg are there cities everywhere on the world map? No. Why not? Because if there were it would look stupid. Look at how the campaign map for Elemental is laid out. The cities are spread out from one another. The cities have a better feel to them because they aren't spammed all over the place like they end up being in a sand box game.
It's really not a complicated fix here either. All that needs to be done to reduce city spam is to increase the rate of the ZOC spread. This will mean more resources get attached to one city which makes that city far more important and valuable in the game, as it should be. They don't need to re-balance incomes or food production or anything like that. Just increase the rate of spread for ZOC and city spam in Elemental would be a thing of the past and the maps once settled by kingdoms or empires would look a Lot Better IMO.

See how close those cities are to one another? A army can walk from one city to another in two turns, maybe three, less if there are roads connecting them. It doesn't lend its-self well to the feeling of a "Mighty Empire" or "Powerful Kingdom". When I laid out those 3 cities, IF I had wanted to snake them out, by the time they all reach level 5 they would be touching each other. In the end the Entire Map turns out to be one large super city...which looks pretty stupid. Also, that's actually Spread Out....you should see the AI cities on the same map. The AI literally builds cities as close together as possible if there are resources close together that it wants. If the AI builds a city next to a iron deposit, and there's a crystal deposit four tiles away, instead of waiting for the ZOC to spread out to get the crystal resource, it goes and builds another city.....four tiles away from the lest city....It's like it's programmed to spam cities every few steps and it ends up looking really lousy and Not looking like the inspiration behind the game design.
Making the ZOC spread out faster could fix these issues very easily with a very limited amount of effort. I really hope they take this into account for the next patch or at least soon, because it makes the world pale in comparison to what it should look like. A lot of effort was put into getting the specific look Elemental has, and it's a good look. The maps are beautiful and have a painted quality that's very pleasing to the eye, but when you spam out cities everywhere it takes a lot away from the look of the world and the maps.