Here's an interview with the Pussycat Dolls, where Jessica comments on Carmit's departue:

How did you react to Carmit’s departure from the group?

Jessica: Well, I think we all felt the same. We miss her, we love her and she’s still part of the family. But we’re also happy because she’s happy and she’s doing what she ultimately wants. She’s been in the group for a long time.