User blog comment:Fallenbladr/Aizens Escape/@comment-5398287-20140817203128/@comment-5398287-20140817220432

I don't think the completion stage of the Hogyoku has anything to do with it, since Urahara stabilized the Visored with an "unfinished" one. Since the Hogyoku only does what the user wishes for, Aizen either didn't think to stabilize Tosen because he didn't know that he was asplode, or he simply didn't care.