Online games are popular because they are social experiences. So it's that the most popular online game, World of Warcraft, has such poor social tools. I just picked up the game again after 16 months and if anything, the social tools are worse now than ever.
The basic social goal in the game is to find people to play with. And for that, you need to join a guild. But how does someone new find a guild? The main way seems to be you get randomly spammed by people saying "join my guild?" Needless to say, the quality of that experience varies. The better way to find a guild is to randomly group up with people you run across until you find someone you like, then stay with them. So pick-up groups are essential.
Here's where WoW got worse. The #1 tool for finding a pick-up group is the "looking for group" channel. It used to be chat there was local to your current zone so you were talking with people roughly your level doing the same things. But a recent patch made the channel global for the whole server. Now the channel is full of random spam and a bunch of people asking for groups way beyond my level.
The spam is bad (there's even a spam filter mod), but the bigger problem is the lack of a place to find people doing things similar to me. The patch has destroyed locality and LFG is now useless.
The other main problem is there's almost never a reason to actually do things with other people until you're level 60. The only group goal for newer players is doing quests together, but it's hard to find quests in common in the first place and the moment someone plays for an hour when their friend is offline they get ahead and the friend can't catch up. Very awkward.
Then again at 6.5M users WoW is doing something right. My theory is there's just enough social contact to keep people happy, but it's really the scripted content and Pavlovian level rewards that keep people going.