That's not entirely true.
SimCity 4 was the last of statistical city simulators. That is to say, if you put down something like a distressed Ong Condos, the game would go "okay, here's 20,778 people in this node in the transportation network, do some network flow and figure out where they work." Newer titles, including the ill-fated SimCity (2013), are agent-based, where they essentially drop in a person and tell them to figure out where they can go or something like that.
As for why SimCity (2013) was a series-ending failure, it was essentially that at every single juncture, EA choose the stupidest possible option, the one that would most guarantee the failure of the series.
The first failure was in the engine itself. AIUI, the developers who came up with the modeling engine knew it wouldn't scale, and never intended for it to actually power a full-fledged SimCity mainline title. EA decided to tell them that it was going to be that anyways. The simulation just didn't scale; the desultory size of the cities was meant to prevent people from attempting to build anything that would cause the simulation to keel over and die--although it's also clear that the max size limit still was too large for the simulation. This is probably where you're getting your idea of perf issues from.
The most famous issue, though, is EA's requirement that the game have multiplayer features to justify being always online (and thus having more intrusive anti-piracy checks). SimCity doesn't lend itself well to multiplayer functionality, and many people correctly assumed that it was a gimmick to justify anti-piracy. Bizarrely, EA tried to claim for a while that one advantage of always-online was to be able to use more powerful servers to do the simulation calculations, but this was never implemented, and the lie was discovered extremely rapidly.
But the single stupidest decision was that EA never put in place enough server capacity to handle the launch. The game would be EA's first always-online flagship release, which meant it would strain their capacity like nothing else they had released ever did. The lack of capacity was repeatedly highlighted as a potential issue in prerelease, and yet was repeatedly ignored. Problems were reported during beta testing and the press preview period, and were still ignored. And launch day came, people experienced several issues, and it still EA like a few weeks to begin to address the issue.
Oh, and you can't forget all the other regular video game release issues like games being released because they need a release date rather than because they're done and things like that.