Japanese people has lots of hair and a single piece of hair has a larger diameter than caucasian hair . So Japanese people want to make their hair look lighter and (they )try to reduce the amount of hair.
Many caucasian hair is thin and has mostly no tension or stiffness. They often want to show that they have lots of hair.
If a caucasian person has a hair cut form a Japanese hairdresser, the hairdresser might make them thinner than necessary. That is why you should choose the right hairdresser in Japan.