User blog comment:Godisme/The Nine Demon Gates/@comment-999343-20131027002215/@comment-7418318-20131027082501

But there's a problem with that. While Hollows can be "created" by other Hollows, there are still plenty of them that are "born" naturally from souls that are unable to reach the afterlife on their own.

So even wiping out every single Hollow currently in existance won't make them extinct. Unless the fundamental "laws of the soul" (for lack of a better term) are changed, Hollows will always exist.

Though I wouldn't put it past Kubo to give Bach a way to do exactly that.