Why did Yujin go on Girls Planet

The show was open to anyone, not only trainees. She's not the only idol who entered the competition but she's the one with the higher profile. The reasons to enter are many. In the case of Yujin, she probably knows CLC is done so she looked for a way to gain some visibility before the official disbandment.

If she joins the final line-up, then she can transition smoothly from CLC to a new group. If she doesn't, then she reminds the viewers that she exists and she's still around.

She joined the survival show as a “Last Chance” sort of deal. We always have at least 1 of those idols who join survival shows because their group wasn’t so successful.

It’s not only for trainees. Active idols from lesser successful groups can also participate. As to why she went:

1. CLC isn’t that successful

2. Cube doesn’t care about CLC

3. CLC members’ contracts are expiring early next year and judging by #1 and #2 we can safely say the group is most likely disbanding soon, so she went in an attempt to get some exposure for herself and maybe redebut in a successful group. If not she still got her exposure. It’s a win-win situation

Because CLC isnt going up

yeah CLC is umm...pretty much done for...