The Tsunderia talents reaped all the benefits of being in a corpo like getting an audience, a model, and support to build their initial personas and now have none of the drawbacks. I honestly see no reason they would chose to kneecap their earnings to join another corpo under their current personas. Auditioning for a large corpo like Niji or Holo and graduating if they got in would make sense.
Step 1: Join Phase/Idol
Step 2: Pay Sakana/Aviel a chunk of your earnings for a marginal bump in popularity at best
Step 3: ????
Step 4: Profit?