User blog comment:Xilinoc/Ch. 591 - Marching Out the ZOMBIES 2/@comment-24509822-20140731013131/@comment-11051098-20140731122009

One thing I wonder regarding Aizen, now that I'm reminded of it:

Yhwach proposed for him to join the Wandenreich, he declined. If Yhwach really wanted him on his side so badly, why didn't he just make it easy and have Giselle zombiefy Aizen? She could easily take control of him just by bleeding a bit on him.

I suppose Kubo has other plans since he didn't use that opportunity.