That’s because most cities have poor quality of life, and once you get out of the twenties, you realize quickly that some breathing room, a safe neighborhood, and a single family home with a yard make you much more happy than having access to a large number of bars, restaurants, and other city amenities that you visit less and less. Most millennials are in their thirties now and as they start families they’re realizing high-density urbanism isn’t all its cracked out to be.

Of course what I’m saying isn’t universal and I think there’s a middle ground with cities that retain low-mid density zoning, but it’s my general observation nevertheless.