This is market forces in action. If more people wanted to live stacked on top of each other then more of those projects would be built. Families with children want to have a backyard, treefort, garage etc. To a large extent space is freedom.
Building more housing in a city is hard. You have to buy out all units in the existing building, and the current residents may be quite reluctant. And actually extending a city is even harder.
An interesting article from a little while back - "How Suburban Sprawl Works Like a Ponzi Scheme" http://www.theatlanticcities.com/jobs-and-economy/2011/10/su...