If you have a plot of land and you can either build a McMansion for one family or an apartment building for 16 families, then (absent heavy-handed regulation) you're going to build whichever one is more profitable, right? And the story of the last ten years is that we build (relatively) more McMansions than we used to, because they are (relatively) more profitable than they used to be, because the rich have (relatively) more money than they used to. What am I missing?