This is not true in Asia. In particular, major Japanese cities, Seoul, and Hong Kong are quite famous for extensive elevated and underground pedestrian networks. The major difference is that density is so high in these areas that they do not run into the problems encountered when implementing in North America, namely that a second level makes the street level dead.

Indeed! It's as well quite needed here in Asia for still being able to walk even when the temperature is either too high (e.g Hong Kong) or too low (e.g Seoul in winter), without having to use cars all the time.