Yiren is so gorgeous and has a lot of star potential. She's young, 19. Yuehua is a Chinese agency. It's been shown many times that the Chinese market is too tempting for both agencies and idols. It seems quite likely that Yuehua is eventually going to have Yiren focus on China. If Everglow becomes popular, it gives Yiren a big head start in China. But she is the center/visual of Everglow and one of the most popular members (I think?). If she leaves, it's going to hurt. Or maybe they're hoping to add Izone Yena to Everglow to make up for the loss?