You might just as well ask why the British are so resistant to them, but a student of mine says that even elsewhere in Asia they have been struck by how much less common umbrellas are than in Japan.
The many possible factors include:
- The long history of umbrellas in Japan
- Japanese trusting weather forecasts more than many nationalities (seen by how few people have umbrellas when there is totally unexpected rain)
- When the number of umbrellas reaches a certain level, you need an umbrella to defend yourself against the other umbrellas
- Haircuts that would be completely messed up by a hat or the rain
- No social pressure against clear plastic umbrellas and cycling with umbrellas
- Rain is often accompanied by high humidity, and coats and waterproof trousers make you sweat, especially if you’re on a bicycle
- The Japanese are generally good at doing what their mothers told them to do, also seen with vests
