Huge tracts of land

Tyler Cowen points to this from Atrios:

I Want A Big Yard In A Walkable Community

But you can't have it! Or, more specifically, if everyone has a big yard the community ceases to be especially walkable. That isn't to say that you can't have developments with yards relatively near to retail, so that there is stuff within walking distance. You can still have corner shops or similar, but having sufficient residential density to support significant neighborhood-serving retail isn't really compatible with everyone has a big yard.

Keep your yard!  Just understand the tradeoff.

Because I've always lived in cities, I don't even understand the utility of the big yards I see in the suburbs.  I get the purpose of a yard for children and dogs to play in, and summers on the patio.  But I don't get the point of the vast expanses of lawn that lie fallow in the more upscale suburbs.  They require vast upkeep for the benefit of . . . looking at green, empty space.  And the tradeoff seems to be a world where you can't get anywhere without driving and your neighbors are distant apparitions.  Am I missing something?  Or do others perceive features where I see bugs?