^Because Berryz were able to preform there solely on their image as "Morning Musume's younger sister group" to be frank. It was back in the days when anything with a MoMusu sticker on it would sell like mad.
Thankfully the H!P Kids were able to shed that image, and the things they accomplish today, are fully on them! Congratulations for C-ute, M-station is a huge deal!