“After in-depth discussion and examination, we have concluded that IMDb’s message boards are no longer providing a positive, useful experience for the vast majority of our more than 250 million monthly users worldwide. The decision to retire a long-standing feature was made only after careful consideration and was based on data and traffic.”  Official announcement 

Personally, I will miss these boards.  Of course, they feature the usual trolls and annoying debates, but  there are also interesting discussions, analysis and theories. I particularly liked to go there after seeing an intelligent movie like Ex Machina, to read some various interpretations and comments. I hope there will be a popular alternative, an other board where you can easily find something on any kind of movies. 

And for the real reason behind the shutdown, I suggest to read this post on Reddit, from someone who worked for IMDb (don’t know if it’s true, but the post makes a lot of sense).