The cost to moderate the boards is probably not insignificant. The revenue they provided (directly) I'm sure made the decision pretty easy to make when looking at it only through the lens of a cold spreadsheet.
I find that weird though; message boards generate a lot of pageviews and are generally rich in content, so they would also generate a lot of advertising revenue.
The message boards on IMDB is nearly the only reason I ever go on IMDB, just after watching a movie. I never go there for their content since there are much better sites out there presenting the info (themoviedb), + there trailers are terrible slow to load (at least where I live) compared to Youtube or even Apple hosted trailers.
I just checked out themoviedb, but there's a lack of information compared with IMDB. For example technical specs of the film like aspect ratio are missing.
Actually, the CPMs are probably fairly low compared to the high-dollar CPMs IMDB gets on its main movie pages. And half the time the discussion isn't really branded per se, it's just banter between fans (or trolls). Forums can create high engagement from a pageview standpoint, but the content isn't really "controlled", so the CPMs are (I'm guessing) rather minuscule in the grand scheme of things.
