Scenarios are extremely easy so the current playerbase loves them. Its impossible to die during one unless you fall asleep. Sadly dungeons are too much effort, apparently...
I think one of the big mistakes of MOP has been abandoning the use of additional 5-mans with later patches -- but not as much as a gear-catchup device, but as a narrative one. Scenarios do some of that work, but I actually thought the ICC 5s and the Hour of Twilight 5s were just really engaging from an immersion standpoint.
Of course, "Halls of Reflection" holds a special place in memory. I can't remember a more dreaded loading screen in LFD history, because you had no idea what sort of ridiculous play you would get, especially back before they nerfed the first room trash (originally you could get spawns with 2 rogues or 2 priests). I also know I'm complaining about this like three years too late, but I knew it was going to be a bad run if the group felt like it would be impossible without hiding in a corner behind Falric or Marwyn. I always tanked it in the archway you enter from -- silences, CC's, etc. On the PTR the only group I did it with cleared it effortlessly tanking it from the Frostmourne dais in the center of the room. People really overcomplicate things sometimes.
Good... they don't need to be wasting their time on stupid 5 mans... max level isn't about stupid dungeons unless you're gearing, but considering the fact we're a couple tier patches into the expansion... all we should be seeing from here is raids... which there aren't enough of. There should be 2 raids per patch, but blizzard doesn't care about the playerbase, which is why the don't pump out content.