As @igrow0ld said ^^^, Sakamichi fandom is basically an underdog here. We can go around and ask people about AKB, and even non idol fans most likely will most lilkely know a thing or two about them. Ask them Nogizaka and they might go "eh?". That, and also in the current era K-Pop is the most well known industry rather than J-Pop. Also, AFA number 1 customers by the end is still those who love Manga/Anime and Anime songs rather than Idol fans.