A strange situation that has been the case for several years now.
I do know that the Japanese have a more limited selection of birth control products than the west e.g the contraceptive pill isn't available there to this day. I don't know about the injection/patch etc but even if they are available they're fairly new so certainly until recently even those in long term relationships would have been relying on barrier contraception. So I suppose the norm must be the use of condoms within relationships, forgoing what is (to me anyway) one of the most enjoyable aspects of a relationship.
Explains why they're at the forefront of condom technology, certainly in terms of sensation.