This doesn't work beyond a small amount. There is only so much land so you have to build up and living in an apartment is a pretty huge sacrifice if you were pr

This doesn't work beyond a small amount. There is only so much land so you have to build up and living in an apartment is a pretty huge sacrifice if you were previously in a single family home with a yard. There is a difference between 'fitting people' somewhere and them being happy. Living in something dense like Tokyo/NYC is not desirable to people who seek cities like Boulder. The other option is to keep expanding outward with single family home lots, but prices in the desirable close areas still shoot way up and traffic gets miserable (see LA).