Board Thread:Questions and Answers/@comment-10797017-20130624101208/@comment-8986886-20130707075720

Yeah, Ikkaku as Captain, with Yumichika as his Lieutenant and Yachiru demoted to 3rd Seat is a decent setup, though I believe Ikkaku's immature decisions might keep him from being promoted.

I simply believe the other Captains see more potential in Renji than they do in Ikkaku, but I'm just guessing here.