The funny thing is, across all MMOs I have played over the years, the trend of an increasingly deteriorating community always tended to really kick off after the introduction of cross server dungeon finders.

I suspect the reason for that is slowly over time it becomes more about cranking the loot treeadmill to 11 instead of maintaining the kind of connections that are really needed for the long term survival of the community. As the cross server dungeon finders reduced the reliance on your fellow server mates for getting things done, and thereby also making it so one didn't have to worry about their own reputation.