I think as far as the BMS goes, they only focused on those 3 that they kept. The other (now-former) BMS members weren't as focused on during the time they were there (they were mostly in the background). The one with the great singing voice, Yui Okamoto, pretty much only had that working for her. Then there was Kotomi Asakawa (not to be confused with the AV star of a similar name) who was "the cute one" but didn't really do much except trying to get a HR during one of the Kawaii Koushien competitions. And then Mami Hojo with that rap or whatever that always resulted in her getting smacked with a fan. And finally, the "kickboxing loli".
They basically kept the leader (Rika), sub-leader (Sayoko) and the "comic relief" (Rion). These three have been pretty much featured ever since their first appearance on the show. It's been mostly Rika and Rion doing the trash-talking most of the time but I guess they couldn't let go of the sexy sub-leader (even though I think the only time Sayoko spoke was during the Kawaii Koushien and the "sexy post contest").
And now I know what being an idol fan feels like....