Just because you're not FORCED to socialize anymore doesn't mean you can't. I make new friends all the time by simply making a choice to be social and talk to people. Because I like making friends and socializing.
The difference is, back in vanilla and TBC, you had to socialize if you wanted to do anything at max level. Queueing systems and the group finder didn't destroy the social aspect of the game, they just made it so that you don't have to anymore if you don't want to, and that's fine if that's your prerogative.
But I will never understand the whiners that cry about the social aspect of the game being dead. What the hell is stopping you from being friendly and talking to people? The answer is nothing but yourself. The problem isn't the game. It's YOU. The game is exactly as social as you make it.