It was there for certain.

In WoW it disappeared when the Dungeon Finder was added, which made social interaction and therefore being nice to each other optional. Before that feature, you had to chat with people in order to form groups for clearing dungeons - a step that the Dungeon Finder conveniently allowed to skip…

Don’t get me wrong, the Dungeon Finder wasn’t the start of it, but it is what accelerated it greatly. Before that social interaction had already been in decline, mostly because everything except for the end-game had been slowly turning into essentially a single-player experience. However, everyone (who stuck to the game) sooner or later reached the end-game content, and had to interact with other players. With the Dungone Finder, this incentive was lost too…

(I am maybe a bit too harsh on the Dungeon Finder - some end-game content was difficult, so you had much higher chances of success if you played with a team you knew well - and therefore had to form/join a guild.)