What is the purpose in that? In a party where there is at least one enchanter, everybody can roll for disenchanting and with that get enchanting materials, even if they don’t have the enchanting profession. They should not have the right to disenchant, but they should go to the auction house and buy the materials. In a dungeon I cannot roll for the skinned mobs for leather, I cannot roll for the ores that are mined from mobs but everybody can roll to disenchant the item. By my opinion it is only right that they can only need and greed. If they need enchanting materials they should go to the auction house.
Purpose: cross-faction trading - and cross-realm, if it were present like in original WotLK Retail - is restricted. So, how would you trade permanent items, e.g. the result of disenchanting mats?
In addition, the value of disenchant materials increased relative to the vendor value of items, especially due to ever lower upgrade value from dungeons over time. Even in pugs, an enchanter disenchanting items and redistributing the mats via trading was already very common. People needed as many reasons as possible to keep running dungeons long after they had all the items they needed.
So, Blizzard changed it so that the disenchant option was automatically available in the loot option, as equivalent to the Greed option, if there was an Enchanter who could disenchant that specific item in the group.
It is a false equivalence to compare to other professions because almost every item can be disenchanted. It would be like saying Enchanters deserve every single piece of loot that people do not Need on because only they could make more use of it.
Man, especially on onyxia where dream shards are usually less then vendor price for the blue item - what exactly is the problem? If there was no DE option, everyone would roll greed, so the chance of you getting the mats is still 20%. I can still mail the greens to my enchanting alt and vendor the blues.
See the difference between disenchanting and gathering professions is you only get leather if you have skinning, but you still get the item if you aren't able to disenchant it.