But why aren't Cims moving into available households? Are there separate demands for dense and light residential like there are in SimCity?
It seems the game likes to keep a few households empty, regardless of what the player does. I assume there's a mechanical reason for this. My
guess is that it likes to keep a buffer so that cims who have their houses destroyed in building projects aren't rendered homeless. I know there is a "Fill the houses" mod to remove this behaviour if you don't like it.
Regarding light and dense, I don't think there are separate demands exactly, but it
seems that you get a more balanced age profile (and gentler death waves) if the city has light as well as dense residential. There's some vague text in the help the says something like "light residential attracts families, dense attracts young adults but they are less inclined to breed", and it seems that there is a higher proportion of families in my light residential zones. If your residents are having fewer than 2 kids per couple on average, you do not have a self-sustaining population and will be dependant on immigration to maintain the numbers.
If anyone from CO is reading, it would be awesome if there could be an info dump on the mechanics of the game. I'd be particularly interested in how households work - what decides where cims live, how they partner up and how they breed. Over the last month I've tried to improve the wiki with some game-mechanics info, but a there's a lot it is difficult to be sure about as things have to be inferred "experimentally" from gameplay.