You have to remember a lot of people on this site are young people without families that prioritize social lives. They haven't related yet that people with kids and careers, etc. are simply not interested in what cities have to offer and that the quality of life in a city is terrible if you have a family compared to what you can get outside of a city in a nice town. Unless you're really rich and can get a huge apartment or condo and can afford to pay for parking or have a driver, etc.
Just look at NYC to find the typical pattern: Young person lives with multiple people in an area like the Lower East Side or Williamsburg (yay social life!), then begins to settle down in a place like Park Slope (just married!) and has a kid (dedicated to urban living) and then another kid comes along and/or the reality of urban living (the schools are awful, it's cramped and expensive, the city offers you nearly nothing since you don't go out like you used to) and the brownstone is sold for a tidy profit and they're off to the NYC suburbs to get more space and a better quality of life to raise a family in. The city is a short commute away still.
Just look at NYC to find the typical pattern: Young person lives with multiple people in an area like the Lower East Side or Williamsburg (yay social life!), then begins to settle down in a place like Park Slope (just married!) and has a kid (dedicated to urban living) and then another kid comes along and/or the reality of urban living (the schools are awful, it's cramped and expensive, the city offers you nearly nothing since you don't go out like you used to) and the brownstone is sold for a tidy profit and they're off to the NYC suburbs to get more space and a better quality of life to raise a family in. The city is a short commute away still.