NewJeans was supposed to be a collaboration between Min Heejin and Bang Sihyuk. Why do you think that changes?

In 2019, when Min Heejin came to Bighit and opened the audition for their first girl group, the group was marketed as a collaboration between Min Heejin, in charge of visuals/concepts, and Bang Sihyuk, in charge of music production. But now, the group is entirely Min Heejin while Bang Sihyuk is working on Le sserafim. Why do you think they stop working together?