Aside from the bureaucratic inertia that all large groups ultimately accumulate have you ever thought that this is by design? Facebook investing resources into really polishing and optimizing the web experience of comments doesn't really get people to use Facebook more. What they really want is for you to post your content, comment on it, and share it all from within the Facebook, and ideally from a highly-optimized Facebook app they completely control.

Facebook Comments aren't designed to be a great experience. They're designed to funnel users into Facebook's ecosystem and to get them to use Facebook more. It's a marketing tool for Facebook.