User blog comment:Xilinoc/Ch. 664 - The Gift/@comment-25897574-20160228212945/@comment-25897574-20160229103622

While that's true, it's extremely difficult to train an ability whose sole purpose is to cause devastation on a large scale without causing bystanders to get caught in it. I can understand using Muken in some cases but some of those mass destruction Bankais would require live targets to test on. And I don't think even Muken could survive Zanka no Tachi.