If i had to guess its probably because smaller penis size on average. If youre taking 10+ dicks a day, better to take 10 smaller ones than take a potential big one then injure yourself and have to rest for the rest of the day.
Most customers I see at both ginzas are asian anyway so they probably don't care about losing a small percentage of their customers.
The truly unlucky ones are Indians since so many girls have no indians
Edit: saw j miwa, I'd say barely A tier for me.
She's good. Description is accurate, and shes pretty. But she seemed quite tired and kind of out of it at times. Next time I wont try the short stay j girls right when they're about to return to japan. Maybe less incentive/more tired at the end of their trip.