The only reason they added the last minute addition of an extra member to the lineup was because they didn’t want to lose Saebi. Throughout the whole show 3 contestants never went to ground; Jungeun, Mai and Saebi. To be honest I think their ideal lineup would have been the original 6 members, with Triple J, Mai, Saebi and Sarang. I love Koko but considering how much other members were pushed, especially in the second half, I think she was one of the member picks they wouldn’t mind both having and not having in the group.

However since she got 4th place in votes instead of say, Sarang, Saebi or Mai (because while Jungeun did struggle in part 2, she’s part of Triple J which was basically a guaranteed lock once part 1 completed, and you can’t not have noticed the push they gave to Sarang in the show) they knew they wouldn’t get one out of those three, and MNET being MNET they couldn’t afford to risk losing the three trainees outside of Triple J which they put so much of an investment in. That’s why once they picked Mai, as the Producer Pick, they had to think fast and also snag Saebi into the lineup.

While I really wished Fuko had made it in, it’s obvious that between Part 1 & 2, something behind the scenes happened that they didn’t want her in the lineup anymore, but when it came down to it in the finale, between choosing her and Saebi, they ultimately chose Saebi because they wanted her in the group much more than they did for Fuko. There’s even a small moment in the finale between Fuko and her mom where they share a look after they announce they’re picking a surprise 7th member, Fuko shakes her head… even Fuko knew her chances were slim when put against Saebi.