Maybe you were talking of hattrick. Japan has many users there. They also have differetn league structures for regions of jpaan, not just Japan.
This is appreciated I think by most users, to play not just in their nation but also their region, but you need lots of success and lots of users as a game to provide that.
I think at best BB can shoot for regional league structure which includes Japan with many of its neighbors.
They don't have different league structures, just that you can select a region (or city) to be your team's home. The only real effects of that are on the weather (though weather is randomized, so picking a region that is rainy IRL won't matter much) and for "derby" matches where both teams are from the same region, the home field advantage does not apply. In some larger countries with a small number of regions, this leads to a lot of derby matches, while in the USA for instance it's still fairly uncommon to run into a derby situation in the higher leagues (lower level teams often forget to pick their region when they sign up and are assigned to Alabama, yee haw).