Community is about communication, that’s obvious right? Richard Bartle in his book "Designing Online Worlds" clearly defines the stages of communities and one of them stands out: community of interest. The members share a common interest and hook up together.
In a MMO it is important that players get connected real soon as they meet people and start friendships. This will be the major reason why they stick to the game later on. If you fail designing your game to support this people will leave with less resistance compared to players who already met friends.
Now lets see what starting players communicate most: questions either about the game mechanics or the game content. The first is quickly resolved when they learned the game and its functions, the second however never stops unless they played through the game's content.
Players ask where a mob is, how a quest is being solved or simply if people want to help them for particular content. Other players will gladly help or players with the same quests team up as they share the same interest. And quickly bonds are forged and friends are met. To design your game to enhance meeting people is key to build up a strong bonded community so people won't leave the game behind easily.
Now game designers think in game mechanics, not in community mechanics. That’s the first mistake they do and unfortunately the negative feedback is coming very late to correct it.
Wrong game mechanics get immediate feedback and correction is mostly easy. Community building mistakes are much harder to read and to analyze.
Lets look at an example. Warhammer Online (WAR) has the tome of knowledge and an intelligent map. Both will tell you where to go for each quest and what to do exactly. In fact the map marks the areas of quests you accepted and also tells you which quest to finish in that region. That eliminates most of the community connecting questions people will ask. That is the number one reason why the chat is so silent in WAR besides the chat interface design.
The consequence: people will not find online friends as easily as in other games. In other words the user interface comforts is limiting the community growth of the game.
Note that World of Warcraft does not support any kind of that feature but there are add ons who do that. But their use is entirely optional and you need to install an Add On to make it work, a major obstacle for starting players. As soon as those players have advanced knowledge they are fit to use it, but at that point they met enough people online to have connected and stay.
So listen designers: carefully consider your game design what it does to community growth and stickiness, not only in term of game mechanics.