They were perfect for telling story of a specific zone or town. They were used for alot of places in MoP and it was pretty well received during it's lifespan.
So why did they quit doing this? It required no tank/heal most of the times, you had fast queue's, the run itself was alot faster then dungeons and you could still get some rewards from it. They were perfectly made really.
So why not just re-introduce it for leveling and endgame?