I will preface this with asking you to take a look at this page: http://www.wowpedia.org/The_Great_Ma...de_quest_chain
You don't need to read everything, just take a glance.
This was a story that started way back at level 15 when you first went to Lakeshire and continued well on until you were at endgame of Vanilla. All it required was a couple trips into BRD and a trip in UBRS. Doing this granted attunement to Onyxia's Lair.
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Where has this epic lore gone? Why were quest chains such as these removed and are no longer created?
Before, people complained that it took forever to get groups together to do these, but that's no longer a problem. With LFD and LFR, you'd be able to complete these quite easily.
Moreover, they would incorporate dungeons into endgame. This combined with new scenarios could really make attunements into something fantastic again.
They tried doing something like this with Wrathion, but that quickly got frustrating and repetitive. They tried something like it with the Thunder Isle and the solo scenarios, but let's be honest: a daily grind is not that interesting.
Examples:
There was no inclusion of the rest of Pandaria. Why not make something where we have to go into Mogu'shan Palace to recover an artifact? Perhaps we can imbue it with the power of the Celestials - by doing the Arena of Annihilation scenario, by doing Temple of the Jade Serpent, by doing the scenario at the Temple of the Crane, by doing the Siege of Nizuhao Temple, we can beef up this artifact to allow us to break through whatever magical barrier is shrouding the Isle of Thunder.
What about in the future? Perhaps in order to defeat this Seventh Sha, we need to get some weapon from the ancient times. Upon [EDIT] unlocking [EDIT] August Celestials, we get a quest to recover a weapon from Taran Zhu in Shado-Pan Monastery dungeon and then we have to defeat avatars of the other 6 Sha that wander around Pandaria like the Warbringers. Each one we destroy charges the artifact until it becomes the ultimate Sha-vanquishing weapon.
TL;DR - the main idea is that people complained due to time commitment and finding players. These arguments or worries are no longer valid with the implementation of LFD and LFR.
For those concerned about alts, you still need to gear up your toon to get into LFR. That effort is no more than what would be required of attunement quest chains.
Would you want to see quest chains like this in the future?