I have to admit that I have no idea what the parent posts are talking about wrt to tribalism, etc. I'm not trying to be dismissive, I literally don't understand.

But I can talk about clubs in Japan :-) I worked in a Japanese high school for 5 years. Students are required to be part of a club. It is part of high school. Most clubs run 6 days a week and students are a member of a club starting from junior high school. Even when people go to university, they invariably join clubs. I don't know if it is required, but after 6 years it is already ingrained.

A club in Japan is very different than a club in North America (I'm Canadian). When you are in school in Canada (at least), you can join many clubs. Most students have many, many hobbies. You are encouraged to try many, many different things. In Japan you have 1 club and that's your hobby. You have exactly 1 chance to change your club -- when you graduate junior high school and join high school (well... you can change again if you go to university).

Because you are forced to practice 1 and only 1 thing, you tend to get quite good at it. Japanese students are very, very good at their hobby (note the lack of plural). This is virtually without exception. Most students (in my experience) absolutely love club. They live for club. It's where their friends are. It's the place where they are accepted. It's the place where they are good at what they do. In the middle of winter, with the wind blowing, and the rain coming down, the only way we could get the tennis boys to go home was to turn off the lights at 8 pm every day. They would show up on Sunday (presumably their day off) and keep at it. That's Japanese club.

Of course some students don't want to go to club. Some students have no interest in a hobby. In my school we had a kind of rotating "club" for students who hated club. One year it was track and field. When we got a student from junior high school who was very serious about track and field, we had to move the non-club club to cooking. Then some students got interested in cooking, so it moved to the English club. Every couple of years it moves somewhere else (and all the teachers flock to volunteer to supervise it because supervising a serious club is a huge amount of work).

It's interesting, though. My school had about 400 students and the non-club club never had more than 60 students in it. Students generally love club. What's more, when a student is in the non-club, you know they have some serious problems. There is not a single happy student in non-club.

Like many things in Japan, the whole concept of a single club that takes up all of your child's free time would not work in other places. Japanese culture is instilled in students at school. Teachers raise the children at least as much as parents do. If teachers think that a parent is doing a poor job, they can and will march over to the parent's house and lecture them for hours on end. I once followed a teacher on his "rounds" visiting parents, and I didn't remove my jaw from the ground for at least a day afterwards.

When you say "being part of a club seems to be incredibly culturally important" you are right. It's the way you live. Even now, my neighbour dragged me off to the karate dojo because he was worried about me. Too much free time is not good for you :-). I have no choice now (even at nearly 50 years old)!