Because he's effectively immortal - can't be killed. The bigger question for me is, why haven't they tried? Perhaps their thought is that trying to do so will just cause him to evolve once again with the Hougyoku still in his chest, but they've got him pretty effectively suppressed. Seems like it would have been pretty nice to torture him for a while and test the limits of his regeneration, which at the very least causes him some major torment.
Though this is all besides the point. I'm hoping that Aizen comes back into the story, which may be the reason Kubo's kept him around. We'll see.
posted over a year ago
He was regarded as a Special War power by Yhwach, which could account for something. Or it could possibly be just another WhatHappenedToTheMouse moment.
But so far, the 'special war potential' thing has held NO MEANING, so I think it's just what they call anyone who poses a threat. But I'm worried that, what with the Quincies getting close to the Soul King, Aizen will show up far closer to his goal than he came after all his plotting through the entirety of Bleach. It would render the entire Arancar Arc pointless, since he lost and STILL ended up in the Soul King's dimension. Unless this was his plan from the start...
He can't be killed, 'while he has the Hougyoku'. If, there was some way to extract it from his body, without the same as what happened to Gin occuring, then it would be alright. I doubt it could happen, but it is an interesting thought.
Yeah, it's possible that such an extraction method exists, but it seems like it's not currently known to anyone in Soul Society, at least... not that everyone in Soul Society knows everything, but you get my drift. And yeah, I'm concerned about that too, exorcist. I want Aizen to come back and have a devious plan, but I really don't want them to put him close to the Soul King immediately.
I would wonder how Kisuke, or why Kisuke, doesn't know a method for extraction, given that he created it - though, Aizen did say that Kisuke failed to master certain aspects of the Hougyoku's existence and Kisuke agreed with him, from what I remember. Of course, that doesn't mean he doesn't know it... and, it might be possible that he's withholding its usage, or something. Of course, I would wonder why he would do such a thing, especially when its likely that he would rather Aizen dead (or would he? maybe 'locked' away is better for Kisuke... who knows...)