You don't need persistent appearances, names, skin tone, homes, or work places to still have complex and decent AI. They track the things that matter like wealth and happiness. By doing this and the method of job and home placement it ensures that you won't get stuck with one building being highly happy with everything else being supremely poor. It distributes the wealth and happiness evenly within the three class brackets. And any buildings that are unhappy will likely only contain the sims carrying the "unhappy data". Which is why somethings can persist in a unhappy state.
Sim City isn't about simulating the life of each individual sim but about simulating the life of each class. You can just follow/track an individual Sim within that bracket.