Then read my lips: C O N T E N T.
More precisely, content that is accessible for all types of players and helps them advance their character without being completely uninteresting (=reasonably challenging).
Is that hard to do? No. Blizzard has done this before in TBC and classic. Consequently, WoW grew to over 10 million players.
In classic players ran 5-man dungeons, UBRS, Molten Core and 20-man raids. The random drop system prevented them from reaching Best-in-Slot anytime soon. The content was challenging, but still quite accessible. Many players complained about unaccessible raids, like AQ or NAXX, but nobody quit due to them. As long as they could advance their own character while running reasonably challenging and accessible content, they were happy!
In TBC players ran dungeons, heroic dungeons and Karazhan. The random drop system prevented them from reaching Best-in-Slot anytime soon. The early badge system didn't hurt much. Many players complained about inaccessible raids, like BT or Sunwell, but nobody quit due to them. As long as they could advance their own character while running reasonably challenging (=interesting) and accessible content, they were happy!
In WotLK players needed to run heroics. They were incredibly grindy, because they needed to be run a lot more often than earlier dungeons. They also were very trivial (=uninteresting) later on. The LFD helped with accessibility, but made them even less interesting. The very accessible respective current raid, combined with the badge system, allowed players to become Best-in-Slot relatively soon.
Nobody complained about inaccessible content, because doing the same raid at higher difficulty seemed rather uninteresting, anyway.
In Cataclysm players need to run a rather small number of heroic dungeons. Even though these are mildly challenging nowadays, they need to be run very often and are so few, that they are not interesting. The LFD helps with accessibility, but makes them even less interesting.
A lot of players cannot raid, because it is too challenging (=not accessible) and stressful. Nerfing an earlier raid tier into the ground doesn't help, because the point system prevents players from reasonably advancing their character this way.
One last thing:
The leveling-by-questing game is impossible to do without outleveling the content. For many players that means that it is not interesting anymore.