[rondrabkin]

Japanese tubs are bigger partly because they are meant to have more than one person.

But in addition they are typically unit bathrooms - like prefab that are installed in a unit in like a day or two. This makes them way cheaper than USA bathrooms. In USA you need contractor, carpenter, plumber, electrician all at diff times and that makes the bathroom really expensive to install.

I assume that if bathrooms were cheaper in the USA we would have bigger/nicer ones. That could be with a bigger bath.