Why? I think this is a rather regressive and nasty step -- there is a lot of good content on those forums (which are, after all, entirely aimed at education).
Why is this forum so toxic? https://forum.duolingo.com/comment/36957067/Why-is-this-foru...
I guess it fell into the StackExchange issue, where beginners or newcomers were not using the search and just asking the same question over and over.
Mods got tired of closing threads, so the users basically self police by marking dupe or telling users to use search.
Let someone else do it, and focus on your key business.