More like "Why didn't we" because overhauling an entire city the way he's describing would probably be an insane amount of work and probably require either the cooperation of most of the real-estate owners, or trying to exercise eminent domain against all of them.
Like, I get the envy Americans—especially those living in suburgatory—have towards cities overseas, but you can't really turn back the clock on that, especially not in a short timeframe. Pretty much every other option for reducing oil dependency will be cheaper and easier.