It shut down for the same reason the forums died down. There's no money in it. I imagine Amazon did an evaluation of how many paying customers would be there ( which unlike people saying they would subscribe rarely turns out that more than a 1000 people would be willing) and there is no way they could recover the cost via advertising. The executives will get the data from deadline or imdb as part of a corporate membership. There is no way an group of 1000 amateurs paying 10 dollars a year would be worth it to run a site like BOM.
Today the internet advertising model is dominated by the toothbrush model pioneered by Google. Only those things are viable that a vast section of people use at least once a day. 10,000 people checking BOM daily isn't viable for advertising.
If it survives its a part of IMDBPro.