User blog comment:Sky-Dragoon-Twilight/Dragons' disappearance theories/@comment-25111584-20140913122606/@comment-9595671-20140913123835

Yeah, i'd like to see how Mashima would pull of having Weiss and Ski being alive.

To answer that last part, I think maybe Dragon Slayer can be learned to be activated at will without the lacrima. So the problem was since Sting and Rogue took a shortcut they didn't develop their Dragon Force's power fully.