They have a function now where you can tag people in comments and reply to them that way, but you are correct in that it breaks down after about 5-10 people get involved in one particular thread.
I'm with CA/CJ here - seems like a way to further corporatize the movie/entertainment industry via social media.
Literally why? There are plenty of trolls on there, sure, but the discussion was nicely individualized to each particular movie. Why would I want to look through a smorgasbord of Facebook comments to discuss likely only the most popular movies?