I can't speak for people that I'm not even one of... but I think that people don't so much like the obvious polish of Sayashi, because it takes away the illusion (which, trust me, is just an illusion!) that the idols are totally 100% normal people who you can happen to see on TV and the stage. The idea that somebody is driven, and hard-working is partly against the idol image.
Another option, is that they want to cheer for an underdog. Which Sayashi obviously isn't. They look at a Kamei, or a Konno, and think "that's the story we want to see on endless loop." Err, more power to them, I guess. (That's why Ikuta got hired?)
But, the group relies on, and needs the made talents. Personally, I'm less (though not entirely un) interested in their story than what they bring to the show. (FWIW, I was a big Konno fan, not for her come-from-behind story, but because she was funny as hell!)
Just to remind you... I'm just guessing.