Nice Neighborhood, Except for the Houses

In my travels, which thankfully are becoming more frequent again, I increasingly find myself returning to a mystifying question: Why has our advanced, modern and wealthy world ceased building beautiful neighborhoods?

I can visit many European cities and find lovely parts of town to walk through. Closer to home, there is no recently created neighborhood in my own Virginia, or nearby Maryland, that can compare to the older homes of Shaker Heights, a suburb of Cleveland. The nicest residential neighborhoods of Washington, such as Georgetown, are typically quite old, predating World War II for most of their attractive structures and sometimes going as far back as the 18th century. Do I need to mention Prague, or the contrast between prewar and postwar German buildings?