Well some dungeons aren't really PuG friendly. PuG = loot seeking. It's rare to go in PuGs to find a nice atmosphere and bond with people and have a nice laugh. When you go with PuGs you're there mainly for loot, or eventually because you're bored or you've never done the place.
Therefore some instances are underused because of that and only done in guild / friend groupes. Not with PuG. It's a great instance none the less and hopefully will be done more often with the new quests.... but still in groupes and probably rarely in PuG.