I wouldn't read too much into it, Japan has a Western style constitution, and the idea of a universal right to free association didn't really start to coalesce

I wouldn't read too much into it, Japan has a Western style constitution, and the idea of a universal right to free association didn't really start to coalesce until the mid-20th century. Japan's constitution happened to get ratified in 1947. If we had to do the US Constitution over, there would probably be freedom to associate codified.