Well, all I know is for me, the closest bonds I formed on an MMO were doing the Chains of Promathia missions with my static for the story at the time. Similar to how those who fight together on a battlefield form a unique, tight knit bond, the same applies when people struggle together. It doesn't exist as much in games like these because there really is no need for people to struggle together. Savage is optional and can easily be done in PF with people you won't see again. All the other content is done in DF, and you DEFINITELY don't see them again. The struggle with a certain group of people on a persistent basis is notably absent. With dungeons, you're lucky if you get a 'hi' from the people in your random group. The rest is just speed running the content, while probably looking at something on your other monitor. There is very little engagement, and most people only do them to reach their weekly tomestone cap.