Fai said:
Because there's a shitload of material to go through?
Aizen's connection to Kurosaki family.
Isshin's past.
Soul King as an Enemy and the truth behind the soul king that made Aizen so desperate to oppose him any means necessary. More so the truth that should have made Urahara do the same.
What Mayuri found in HM.
Zeroth Squad and the shady "promotions" into it.
Royal Guard.
The secret and reason behind -getsu swords.
Thats just off the top of my mind, I am sure there's more.
And instead of using any 1 of these plot points (which would have been more important and much more interesting than this arc), Kubo decides to waste time on this Fullbring nonsense.
It takes time.
Tsuki's ability takes some time to work. Remember CHad and Inoue? Most likely thats all we will see of their fight.
Not for Ginjou, within a few moments of being cut, he reverted back to his old self.