They are popular in Asia because relatively speaking Asia is poor.
Just like the flying pigeon bike was massively popular in china back in the 70's, I even saw one being ridden at Cranfield university by a Chinese masters/doctoral student in the late 70's early eighties.
The overall point was that bikes can be made to work, Asia is a large scale example, although as you say, not necessarily by choice. The Netherlands, and increasingly other parts of north west Europe are another example.
No, Japan is one of the richer countries on the planet per-capita, and bicycles are very popular there. They're popular because they're cheap and simple and they have excellent public transit for longer distances and they don't have to worry much about thieves like in crappier countries. And as a result of people biking and walking more, almost no one there is fat, unlike America where the majority of the population is obese (not just overweight).
