I know part of the issue is that they're still tying themselves to a console release, so they can't do everything with the environment that they'd be able to with a pure PC release. I expect they also burned no small number of dev cycles on the console side, too.

Though, I'm of the opinion that PC tech has moved so far beyond console tech now that something on the scale of an MMO should probably be exclusively for the former, and not the latter.