Why did Yena go solo instead of join Everglow?

^above

I'm not a huge IZ*ONE fan but I got into Yena's songd recently. I also liked Everglow's biggest songs. I always thought Yena would be a great addition to Everglow so I don't really understand why they decided to separate the acts. At least, I thought they could give Yena solo music on the side. It feels like girl groups are more sustainable than solo acts in general. Do you think it was the right decision?