Anyone who isn't a DPS class probably wants to see their cool new animation sometime. Due to the offensive focus of the game, people almost never get to see the tank or healer limit breaks. If you're on the bleeding edge of content, you might see them more often, but DPS(specifically MDPS) always gets to hammer their cool limit break button while tanks and healers look at the bar forlornly, and since LB3 only comes up in 8 man content it's much harder to justify blowing it just to see what it does, for once.