"The developers realize that there is still an audience for Burning Crusade level difficulty Heroic dungeons. Challenge modes were designed to be harder content, but the focus is on speed and not as much on having to use as much CC, so they don't capture the essence of Burning Crusade era Heroics."
http://www.mmo-champion.com/content/...es-Blue-Tweets
they released timed runs were bad because they didnt capture what people wanted.