I agree that with OP that the large number of people in Japan may be part of the explanation. But I think there are a few Japanese specific explanations at wel

I agree that with OP that the large number of people in Japan may be part of the explanation. But I think there are a few Japanese specific explanations at well. For instance, - In Japan, sleeping in public is more common (0) - The workplace is more formal, meaning more men in suits (1) - Drinking after work is very common in Japan (2) This means that sleeping outside is less taboo for salarymen, that they are more likely to wear a suit to work and they are more likely to head to the bar straight after work while still in their suit. In other places, I image people might change before heading to the bar or wear something different to work in the first place or might have more inhibition about sleeping in public. (0) https://www.nytimes.com/2016/12/16/world/what-in-the-world/japan-inemuri-public-sleeping.html https://www.nytimes.com/2016/12/16/world/what-in-the-world/j... (1) https://www.businessinsider.com/differences-between-japanese-and-american-work-culture-2018-3 https://www.businessinsider.com/differences-between-japanese...] (2) https://en.wikipedia.org/wiki/Nomikai https://en.wikipedia.org/wiki/Nomikai