In contrast: creating Slums in Ceasar, Pharaoh, or Tropico is an explicit strategy. Why? Because low-income industries (such as mining or farming) cannot afford better housing. The slum is the best that you can give that population as a leader.
In Ceasar, they're extremely cheeky about the highest class of citizens. Only plebeians work. If you "upgrade" housing to the point of attracting patricians, you LOSE workers (because patricians don't work!!). There are entire strategies in the game about attracting as many plebeians (working-class) citizens needed to have a functioning economy, but then converting the excess workers into Patricians for higher-tax collection.
As such, you need to keep the plebeians purposefully at a lower class to keep your industrial sector working. If you convert everyone into patricians, no work would get done at all. Its a challenge to build road-networks that separate the housing units, but provide the workers needed to serve the upper class (ex: services such as bath-houses and marketplaces are run by plebeians, but should be placed inside of Patrician neighborhoods)