In Produce 101, I don’t understand why t…

In Produce 101, I don’t understand why they keep trainees in F class (even after reevaluation) on the programme. I feel like they’re pretty much useless. I’m not sure if that’s how it works in Produce X 101 now when they get X, but if it is, I feel like it’s much smarter than keeping them in and bringing the other trainees down in their groups because they won’t get as many votes.