Board Thread:Theories Discussion/@comment-16798306-20130307124756/@comment-6192846-20140425223435

The only info we can confirm is that the Demon of Lust had gone missing from the Venom Sword sometime between the time it possessed Kyle and that Elluka picked it up from Keel. Considering Kyle's possession by both DoL and DoP were planned out by Prim and Abyss I.R., Praefacio of Blue would be the best bet to find an answer on why it disappeared from its vessel.

Assuming there is no explanation there and the Demon of Lust is stil AWOL from its vessel, then that mystery will likely carry over into the upcoming novel release(s) for Sloth. If the Demon still hasn't returned to its vessel by the time Gallerian added it to his collection, I still think that's the reason it won't awaken.

If that's the case, the same thing may have happened to Kayo's Scissors (though now that we know there are two pairs of scissors for the one vessel, that adds a lot more options to speculate on).