Because Ichigo constantly drops in strength after every powerup so that the enemies can seem to be difficult fights without instantly killing anyone who isn't Ichigo.
Tite Kubo fails hardcore at keeping track of how strong his characters are.
Quote:
Originally Posted by *zErOfOx  have you ever seen a main character lose a serious battle ?  |
Yes, even Bleach itself once did so, way back when Byakuya nearly killed Ichigo.