Eh what? the answer is glaringly obvious why, i can form a group in 10 seconds with 'LF9M TD', the LFR tool insists you need 2x Tanks, 2x Healers, 5x DPS and 1x Support.
Nobody is going to hang around waiting for people to correctly click a role, you only need 2 Tanks for spider boss, i can solo heal the entire Raid and if we want a speed run, don't use a support so for people that are chain running TD to upgrade gear it's more time effecient to get a group in chat, instant Raid formed in less than a minute.