Posts are down to their lowest levels since the 90s (if I'm reading this graph right).[1] Also, someone at Y! probably figured out how much it cost to run the infrastructure and maintain the code.
That graph is biased in that it only covers discovered groups and only half have been discovered (older groups are likely more likely to have been discovered). Assuming it's NOT biased something happened in the 2nd half of 2014 to destroy traffic to Yahoo Groups.
> Assuming it's NOT biased something happened in the 2nd half of 2014 to destroy traffic to Yahoo Groups.
That is the time when Yahoo! Groups fucked up their DMARC implementation: