It's more than just a density problem. People need to be locally consistent.
They need a place that caters to their culture(including the town or city itself - micro culture) - they need a place to hang out with people of like mind, they need hobbies and places to go, they need restaurants, events, parks, quiet places, loud and busy places, areas to connect with nature, areas to focus on business or meet fellow enthusiasts. It's not a numbers game .... it's human emotions and reality.
we need hospitals and daycares and public pools, arcades, shops, zoos, heritage sites, pop ups, concerts, etc ...
it's more than just walls + plumbing and electrical codes.....