If anybody was wondering why Shunsui and Ukitake or even Yamamoto for that matter aren't going Bankai even when they are about to get killed, it's because the scriptwriters are limited to using only those moves and techs which Kubo has revealed till date.
However, they messed up in one place. Soifon definitely can't do as she please with her Bankai. The recoil is supposed to kill her unless precautions are taken but she just used it so comfortably in this arc- it was COOL!














