This is not true at all.
The last SimCity was terrible in a lot of ways (online requirements, small areas, bugs, etc) but it had the best simulation out there: an one 1:1 car / population that made city and road planning a true joy for the nerdiest players like me. Literally every aspect of city planning had an impact on that simulation, and you could follow every car and knonw it was there for a reason. This means that if you have a really bad traffic state every aspect of your city goes on fire.
On the other hand Cities skyline has a lot of other cool factors but traffic simulation comes really short. It is just derived from statistics of the city but there is no 1:1 link to be found, so you can just guess what aspects of the city has some coefficient on the traffic algorithm, and the worst part is that if you happen to plan something really wrong, well, nothing happens. Cars and utility veichles litterally start to DESPAWN from the road and the traffic jam goes puff. Yes the statistics go down a bit, but everything else goes on like nothing ever happened. That was the deal breaker for me
That's why you have to use SimCity 4 Deluxe with Network Addon Mod. It's a whole new game and it's actively developed since 2004, with developer momentum picking up.
This is not true at all. The Skylines traffic model is agent driven. The residences have residents who travel to shopping, and the industries have to receive raw materials and ship finished goods to retail or export. Despawning does occur, but if there is too much despawning and the industries cannot get their raw materials or deliver their goods, they will complain and eventually close. Same if the commercial zones can't receive deliveries or get customers. Garbage trucks need to be able to complete their rounds or garbage piles up, and dead bodies need to be picked up. There are map views that show exactly what trips are using what roads, and you can trace a vehicle from source to destination.
Despawning can be thought of as what happens in any city when the traffic grid is overwhelmed: some travel simply does not occur at all. People stay home or they do not transact business because traffic is too bad.
It's not a perfect traffic model - for instance, residents don't really need to get to work or school; they are just teleported there if there's no route. Cars do not need to be parked. So a city sim with the Factorio devs' obsession with optimization would be great. But it's not accurate to say that Skylines traffic is just derived from the statistics of the city.
If I remember correctly garbage trucks were exactly the only 1:1 vehicle represented on the traffic, so yea, a part from that you just expanded my point. Just derivative statistics that goes down and up. Nothing like a real 1:1 simulation like the SimCity one
From what I've seen, in C:S, all vehicles are 1:1.
Vehicles will despawn, though I'm not sure what it's based on. Dunno if it's total time on the road, or if it's based on being stuck in a jam for too long, or what.
In any case, a vehicle that despawns is a cancelled trip. A commercial building won't receive its goods. A worker won't get to work. If your city's traffic is bad, a significant number of trips won't complete, and your commercial districts will abandon due to lack of workers or lack of goods, industries will abandon due to lack of buyers or lack of raw materials, and residential will abandon due to unemployment.
Despawning affects service vehicles too, so if they're frequently being despawned, garbage piles up, people get sick and die, crime goes up, etc.
There are mods that will disable despawning. But in a large city, this will likely make your roads turn into gridlock. Once this happens, nobody reaches their destination, and your city quickly goes to shit.
There's a very popular, easy-to-install mod that removes automatic traffic despawning and allows you to make a bunch of other behavioral tweaks to traffic.
