User blog comment:Omega natsu2/Chapter 368: The Third Seal, Predictions./@comment-4933386-20140120162841/@comment-7418318-20140121094730

Probably because anyone how knew where Face was and how to detonate it once it's unsealed died before they ever got the chance to use it.

Or they might have thought it wouldn't work against Dragons.

Or the Dragons knew about Face and either destroyed it, or guarded it.

Or the cowards on the council just panicked and fled without even thinking about Face.