Some critical point is reached. Sniping ensues. The thread -- or the roleplay -- becomes a series of personal disputes. These manifest as people posting back-and-forth, endlessly, irrelevantly, ad nauseam. Any attempt to draw a line in the sand results in the tedium of analysis and argument.
There must be a framework for resolving disputes, otherwise it goes on, and on, and on. But the burden of fidelity falls upon developer and player. The professional actor always acts the role, even if they do so in character. If one starts as a peasant, one starts as a peasant. You work your way up from there. Progression must be based upon time invested in the game, otherwise it will be either outright unfair, or it will be interpreted as being unfair by someone.
If we translate the personal dynamics of forum disputes to the game world, it becomes apparent that roleplay must be initiated, maintained and enforced by game mechanics for the same reason that there are posting guidlines on the forums. And lines on the roads. The reason that this is argued against so harshly is basically always form of greed, some subjective non-obvious abstraction of game property/status/whatever re ego of player.
To finally answer XIllix's original question: It has been a combination of roleplay/settings/property disputes varying widely from player to player, combined with disappointment in unimplemented features. The tendency of players to drop out to look for other games to try and settle into, becomes the added watershed that holds the online numbers down.
But of course, all of this misses a great and obvious point. That we are still here, TRYING to have a civilized discussion and game environment. So there must be something good buried in all of this. Right?