The story goes like this
In the times of "no transmog" everyone was ugly. So it was prestigious to have a raid tier set.
This created a cycle of people watching players with said tiers and them wanting to raid to be like them.
It was an endless cycle each expansion to "be able to be cool i need a complete tier set".
This was the main incentive for raiding. People wanting to be cool looking.
Now? There is transmog and people dont care about nothing no more because everyone looks cool.
This destroyed the cycle of PvE incentive and quest for prestige.
Meaning, there is no incenitve no more for raiding. Only item level...but who cares about that? Heroic/Mythic Raiders, a minority.
This thread is related to this one
(Just an example on how to give prestige back)
http://www.mmo-champion.com/threads/...-New-Tier-Sets