Blizzard gave premade raids another shot when Ashran was first launched, but they were quickly reminded that premade raids vs. pugs is a very poor PvP experience. So Blizzard disabled premade raids.
Holinka tweeted:
https://twitter.com/holinka/status/646509604638035968
https://twitter.com/holinka/status/646509965465616384
https://twitter.com/holinka/status/646510211453194240
https://twitter.com/holinka/status/646510398091362304
Later on, Holinka once again emphasized they don’t like premade raids in random bgs.
https://twitter.com/holinka/status/312067433181618176
Unfortunately, those tweets were lost when Holinka deleted all of his old tweets.
But, it’s not like premade raiders listened to him even when the tweets were up.